Question

A sandwich costs 5:70 and a piece of fruit costs 2:15 if you have a 20 bill, how much change will you get ?

Answer 1

Well if you buy only 1 of each, it would cost you 7.85 in total. if you subtract that from 20, it equals 12.15.
you can also make it a linear equation if you want more or less than 1 fruit and or sandwich
s=sandwich
f=fruit
5.7f+2.15f=20