Explanation:
let x be the price of the adult ticket and y the price of child ticket
so
3x+7y=132
4x+7y=141
from the first equation 7y=132-3x
lets replaxe this from the second equation
4x+(132-3x)=141
4x-3x=141-132
x=9
so knowing that 7y=132-3x
7y=132-3*9
7y=105
y=105/7=15
so finaly the adult ticket cost 9 dollars and child ticket cost 15 dollars