Yarin's gross pay for the year was $3,500. The federal income tax withholding from his pay was 9% of his gross pay. Yarin determined the federal income tax he owes is $115. How much of a refund can Yarin expect?

A.200
B.315
C.3035
D.3185

52 \43 i don't know this i tried

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

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