how do i solve this

Question

Luke is selling tickets to a school play. each adult ticket cost $10 each and child's ticket cost four dollars. Luke sold 87 for the total of 678 how many tickets of each type did Luke sell?

Answer 1

I will assume 678 means $678.

Let x = the number of adult tickets sold

Let y = the number of children's tickets sold

x + y = 87       x = 87 - y

10x + 4y = 678

10(87 - y) + 4y = 678

870 - 10y + 4y = 678

-6y = -192

y = 32 children's tickets

x = 87 - 32

x = 55 adult tickets