investment tax credits have been deferred by the regulated utility subsidiaries and are being amortized to income over the average estimated service lives of the related assets .
the company recognizes accrued interest and penalties related to tax positions as a component of income tax expense and accounts for sales tax collected from customers and remitted to taxing authorities on a net basis .
see note 14 2014income taxes for additional information .
allowance for funds used during construction afudc is a non-cash credit to income with a corresponding charge to utility plant that represents the cost of borrowed funds or a return on equity funds devoted to plant under construction .
the regulated utility subsidiaries record afudc to the extent permitted by the pucs .
the portion of afudc attributable to borrowed funds is shown as a reduction of interest , net on the consolidated statements of operations .
any portion of afudc attributable to equity funds would be included in other , net on the consolidated statements of operations .
afudc is provided in the following table for the years ended december 31: .

2018
2017
2016
Allowance for other funds used during construction
$24
$19
$15
Allowance for borrowed funds used during construction
13
8
6

environmental costs the company 2019s water and wastewater operations and the operations of its market-based businesses are subject to u.s .
federal , state , local and foreign requirements relating to environmental protection , and as such , the company periodically becomes subject to environmental claims in the normal course of business .
environmental expenditures that relate to current operations or provide a future benefit are expensed or capitalized as appropriate .
remediation costs that relate to an existing condition caused by past operations are accrued , on an undiscounted basis , when it is probable that these costs will be incurred and can be reasonably estimated .
a conservation agreement entered into by a subsidiary of the company with the national oceanic and atmospheric administration in 2010 and amended in 2017 required the subsidiary to , among other provisions , implement certain measures to protect the steelhead trout and its habitat in the carmel river watershed in the state of california .
the subsidiary agreed to pay $ 1 million annually commencing in 2010 with the final payment being made in 2021 .
remediation costs accrued amounted to $ 4 million and $ 6 million as of december 31 , 2018 and 2017 , respectively .
derivative financial instruments the company uses derivative financial instruments for purposes of hedging exposures to fluctuations in interest rates .
these derivative contracts are entered into for periods consistent with the related underlying exposures and do not constitute positions independent of those exposures .
the company does not enter into derivative contracts for speculative purposes and does not use leveraged instruments .
all derivatives are recognized on the balance sheet at fair value .
on the date the derivative contract is entered into , the company may designate the derivative as a hedge of the fair value of a recognized asset or liability ( fair-value hedge ) or a hedge of a forecasted transaction or of the variability of cash flows to be received or paid related to a recognized asset or liability ( cash-flow hedge ) .
changes in the fair value of a fair-value hedge , along with the gain or loss on the underlying hedged item , are recorded in current-period earnings .
the gains and losses on the effective portion of cash-flow hedges are recorded in other comprehensive income , until earnings are affected by the variability of cash flows .
any ineffective portion of designated cash-flow hedges is recognized in current-period earnings. .

Question: Analyse this data from a financial earnings document. by how much did allowance for other funds used during construction increase from 2016 to 2018?
Choices:
-0.6
135
9
0.4
0.6
Correct choice index: 4