Answer:
movie theatre = 20 hours
car wash = 10 hours
Explanation:
this would be solved using simultaneous equation
let a = hours worked in theatre
b = hours spent wash cars
15a + 18b = 480 eqn 1
a + b = 30 eqn 2
multiply eqn 2 by 15
15a + 15b = 450 eqn 3
subtract 1 from 3
3b = 30
b = 10 hours
substitute for b in eqn 2
a + 10 = 30
a = 20 hours