Let a represent the number of adult tickets sold
Let c represent the number of children tickets cold
Equation for total sales:
8c+18a=8,400
Equation for how the tickets relate:
a=2c+50
ANSWER
8c+18a=8,400
STEP 1: Add -8c on both sides
18a=(-8c)+8,400
STEP 2: Divide both sides by 18
18a / 18 = -8c+8,400/18
a=-4/9c + 1,400/3