Solve for x: 1/6 + 1/6 + 1/6 + 1/6 = x/24.

1st: Divide BOTH sides by 6
It'll cancel out all the first fractions, leaving you with 1 + 1 + 1 + 1 = 6x/24

2nd:
Divide BOTH sides by 24 
It'll cancel out the last fraction leaving you with: 24 + 24 + 24 + 24 = 6x

3rd: 
Add up all the 24's to get 96 = 6x

4th
Divide BOTH sides by 6
Leaving you with 16=x

That would be 16/24 because 1/6+1/6+1/6+1/6=4/6 and 4/6=16/24

No solution : there is no number of boxes that she bought