The equation is for when you compound annually is

A=future amount
P=initial amount or principal
r=interest rate in decimal form
t=time in years
so
A=A
P=3500
r=7.5%=0.075
t=13


use your calculator
A=8961.4457
round to nearest dollar
A=$8961
that's how much the investment will be worth after 13 years
Answer: Choice D
Explanation:
The increase of 9.8% rounds to 10% when rounding to the nearest ten
An increase of 10% would use the multiplier 1.1
Think of it like saying 1 + 0.10 = 100% + 10%
Similarly, the 5.1% rounds to 5% and an increase of this amount will use the multiplier 1.05
So if we started with 20 items, then 20(1.1)(1.05) is the expression that estimates an increase of 10% followed by an increase of 5%. The order doesn't matter (so you could increase by 5% first, then 10% later).
Yes, you can add a negative and a positive when doing like terms.