Alright well for (A) you will round $5280 to $5300. Then you multiply $5300 by 28.
For (B) you just round up. So again $5280 rounds up to $5300.
Get n to one side
-1/5=-2/5n
divide both sides by -2/5
n=1/2
let's notice, this is a Cube, namely all equal sides, and mind you it has 6 sides, Check the picture below.

Answer:
90
Step-by-step explanation:
90/10= 9
90/5= 18
No number larger than 90 would work.