Question

the total amount in pesos of 30 coins consisting of 5-peso coin and 10-peso coin is php 215 . how many coins of each type are there?

Answer 1

if there were x 5-peso coins, then the rest (30-x) are 10-pesos. Adding up the value, you get
5x + 10(30-x) = 215
now solve for x

Answer 2

5x+10(30-x)=215
5x+300-10x =215
5x-10x=215-300
-5x/5 = -85/5
x= 17