So i think u subtract how much money the person got and then subtract the answer by his pay.
Area of the entire rectangle 
Solution:
Area of the blue box = length × width

Area of the blue box 
Area of the pink box = length × width

Area of the pink box 
Area of the green box = length × width

Area of the green box 
Area of the orange box = length × width

Area of the orange box = 24
Total area of the rectangle 

Area of the entire rectangle
Let T = total cost
Let 8c = total amount of children tickets
Let 12a = total amount of adult tickets
T = 8c + 12a