note 18 2013 earnings per share ( eps ) basic eps is calculated by dividing net earnings attributable to allegion plc by the weighted-average number of ordinary shares outstanding for the applicable period .diluted eps is calculated after adjusting the denominator of the basic eps calculation for the effect of all potentially dilutive ordinary shares , which in the company 2019s case , includes shares issuable under share-based compensation plans .the following table summarizes the weighted-average number of ordinary shares outstanding for basic and diluted earnings per share calculations. .
[['in millions', '2017', '2016', '2015'], ['weighted-average number of basic shares', '95.1', '95.8', '95.9'], ['shares issuable under incentive stock plans', '0.9', '1.1', '1.0'], ['weighted-average number of diluted shares', '96.0', '96.9', '96.9']]
at december 31 , 2017 , 0.1 million stock options were excluded from the computation of weighted average diluted shares outstanding because the effect of including these shares would have been anti-dilutive .note 19 2013 commitments and contingencies the company is involved in various litigations , claims and administrative proceedings , including those related to environmental and product warranty matters .amounts recorded for identified contingent liabilities are estimates , which are reviewed periodically and adjusted to reflect additional information when it becomes available .subject to the uncertainties inherent in estimating future costs for contingent liabilities , except as expressly set forth in this note , management believes that any liability which may result from these legal matters would not have a material adverse effect on the financial condition , results of operations , liquidity or cash flows of the company .environmental matters the company is dedicated to an environmental program to reduce the utilization and generation of hazardous materials during the manufacturing process and to remediate identified environmental concerns .as to the latter , the company is currently engaged in site investigations and remediation activities to address environmental cleanup from past operations at current and former production facilities .the company regularly evaluates its remediation programs and considers alternative remediation methods that are in addition to , or in replacement of , those currently utilized by the company based upon enhanced technology and regulatory changes .changes to the company's remediation programs may result in increased expenses and increased environmental reserves .the company is sometimes a party to environmental lawsuits and claims and has received notices of potential violations of environmental laws and regulations from the u.s .environmental protection agency and similar state authorities .it has also been identified as a potentially responsible party ( "prp" ) for cleanup costs associated with off-site waste disposal at federal superfund and state remediation sites .for all such sites , there are other prps and , in most instances , the company 2019s involvement is minimal .in estimating its liability , the company has assumed it will not bear the entire cost of remediation of any site to the exclusion of other prps who may be jointly and severally liable .the ability of other prps to participate has been taken into account , based on our understanding of the parties 2019 financial condition and probable contributions on a per site basis .additional lawsuits and claims involving environmental matters are likely to arise from time to time in the future .the company incurred $ 3.2 million , $ 23.3 million , and $ 4.4 million of expenses during the years ended december 31 , 2017 , 2016 and 2015 , respectively , for environmental remediation at sites presently or formerly owned or leased by the company .in the fourth-quarter of 2016 , with the collaboration and approval of state regulators , the company launched a proactive , alternative approach to remediate two sites in the united states .this approach will allow the company to more aggressively address environmental conditions at these sites and reduce the impact of potential changes in regulatory requirements .as a result , the company recorded a $ 15 million charge for environmental remediation in the fourth quarter of 2016 .environmental remediation costs are recorded in costs of goods sold within the consolidated statements of comprehensive income .as of december 31 , 2017 and 2016 , the company has recorded reserves for environmental matters of $ 28.9 million and $ 30.6 million .the total reserve at december 31 , 2017 and 2016 included $ 8.9 million and $ 9.6 million related to remediation of sites previously disposed by the company .environmental reserves are classified as accrued expenses and other current liabilities or other noncurrent liabilities based on their expected term .the company's total current environmental reserve at december 31 , 2017 and 2016 was $ 12.6 million and $ 6.1 million and the remainder is classified as noncurrent .given the evolving nature of environmental laws , regulations and technology , the ultimate cost of future compliance is uncertain. .

Question: considering the years 2015-2017 , what is the average expense for environmental remediation at sites , in millions of dollars?
Answer: 10.3
Explanation: it is the sum of all environmental remediation expenses during these years , divided by three ( number of years ) .