Maria started with 37 boxes.
Given:
7 boxes bought
half of the boxes were destroyed in the fire.
22 boxes left
Find the beginning number of boxes.
Let x be the beginning number of boxes.
(x + 7)/2 = 22
2((x+7)/2) = 2(22)
x + 7 = 44
x = 44 - 7
x = 37
To check:
x + 7 = 37 + 7 = 44
44 * 1/2 = 22
22 = 22