republic services , inc . notes to consolidated financial statements 2014 ( continued ) high quality financial institutions . such balances may be in excess of fdic insured limits . to manage the related credit exposure , we continually monitor the credit worthiness of the financial institutions where we have deposits . concentrations of credit risk with respect to trade accounts receivable are limited due to the wide variety of customers and markets in which we provide services , as well as the dispersion of our operations across many geographic areas . we provide services to small-container , large-container , municipal and residential , and energy services customers in the united states and puerto rico . we perform ongoing credit evaluations of our customers , but generally do not require collateral to support customer receivables . we establish an allowance for doubtful accounts based on various factors including the credit risk of specific customers , age of receivables outstanding , historical trends , economic conditions and other information . accounts receivable , net accounts receivable represent receivables from customers for collection , transfer , recycling , disposal , energy services and other services . our receivables are recorded when billed or when the related revenue is earned , if earlier , and represent claims against third parties that will be settled in cash . the carrying value of our receivables , net of the allowance for doubtful accounts and customer credits , represents their estimated net realizable value . provisions for doubtful accounts are evaluated on a monthly basis and are recorded based on our historical collection experience , the age of the receivables , specific customer information and economic conditions . we also review outstanding balances on an account-specific basis . in general , reserves are provided for accounts receivable in excess of 90 days outstanding . past due receivable balances are written-off when our collection efforts have been unsuccessful in collecting amounts due . the following table reflects the activity in our allowance for doubtful accounts for the years ended december 31: .

2017: balance at beginning of year: 44
additions charged to expense: 30.6
accounts written-off: -35.7
balance at end of year: 38.9
2016: balance at beginning of year: 46.7
additions charged to expense: 20.4
accounts written-off: -23.1
balance at end of year: 44
2015: balance at beginning of year: 38.9
additions charged to expense: 22.7
accounts written-off: -14.9
balance at end of year: 46.7

restricted cash and marketable securities as of december 31 , 2017 , we had $ 141.1 million of restricted cash and marketable securities of which $ 71.4 million supports our insurance programs for workers 2019 compensation , commercial general liability , and commercial auto liability . additionally , we obtain funds through the issuance of tax-exempt bonds for the purpose of financing qualifying expenditures at our landfills , transfer stations , collection and recycling centers . the funds are deposited directly into trust accounts by the bonding authorities at the time of issuance . as the use of these funds is contractually restricted , and we do not have the ability to use these funds for general operating purposes , they are classified as restricted cash and marketable securities in our consolidated balance sheets . in the normal course of business , we may be required to provide financial assurance to governmental agencies and a variety of other entities in connection with municipal residential collection contracts , closure or post- closure of landfills , environmental remediation , environmental permits , and business licenses and permits as a financial guarantee of our performance . at several of our landfills , we satisfy financial assurance requirements by depositing cash into restricted trust funds or escrow accounts . property and equipment we record property and equipment at cost . expenditures for major additions and improvements to facilities are capitalized , while maintenance and repairs are charged to expense as incurred . when property is retired or .

Questions:
what was the change in the account balance in the allowance for doubtful accounts from 2016 to 2017?
and what was this change as a percentage of that account balance in 2016?
and as of december 31 of the last year of that period, what was the amount from restricted cash and marketable securities for the supports our insurance programs for workers 2019 compensation , commercial general liability , and commercial auto liability?
what was the total of that restricted cash and marketable securities?
what percentage, then, of this total, did that amount represent?

Answers:
-2.7
-5.8%
71.4
141.1
50.6%