Answer:
Step-by-step explanation:
Let b represent the number of boxes of cookies sold the first week. Then b+5 boxes were sold the second week, and 2(b+5) boxes were sold the third week. The total sold was ...
b +(b+5) +2(b+5) = 431
4b +15 = 431 . . . . . . simplify
b = (431 -15)/4 = 104 . . . . . subtract 15, divide by the coefficient of b
First week: b = 104
Second week: b+5 = 109
Third week: 2(b+5) = 218