How do you know if a sum or product will result in a rational or irrational number?

Astore sells two types of radios. one type sells $87 and the other for $119. if 25 were sold and the sales were $2495, how many of the $87 radios were sold a) 5 b) 20 c) 15 d)10

Is there an x intercept in the equation 60*1.15^x

Paco orders an ice cream for $1, but realizes his wallet is at home and he only has 3/20 of $1 with him. if his mom pays the remaining 7/20 of the dollar, how much will she pay? $0.05 $0.15 $0.85 $0.95