Question 1068156
y=ab^x, where a here is the amount deposited, and x is the number of compoundings.
I'd round to two decimal places, since it is money.
The figures are correct.
The second is more than the first because more was deposited.
The tripling time of money in years is ln3/interest rate as decimal number, because p/po=e^rt and ln (3), which is the ratio=rt, so ln3/r=t
here in 10 years ln3/.15=7.32 years so that tripling just occurs for the second, but the first has quadrupled.
Quadrupling is doubling of doubling, and the rule of 70 is used there, where 70 over the rate (in per cent) is the doubling time--70/15=4.67 years, so this doubled and again doubled.  That is consistent with $60,000.