180 stickers are in 3 boxes.
The second box has 3 times as many stickers as the first box.
The third box is 40 less than the first box.
How many less stickers are there in the first box and the third box than in the second box?
Choose the box with the least stickers to be 1 u.

Number of stickers in the third box = 1 u
Number of stickers in the first box = 1 u + 40
Number of stickers in the second box = 3 x (1 u + 40) = 3 u + 120

Total number of stickers
= 3 u + 120 + 1 u + 40 + 1 u
= 3 u + 1 u + 1 u + 120 + 40
= 5 u + 160

5 u + 160 = 180
5 u = 180 - 160
5 u = 20

1 u = 20 ÷ 5 = 4

Number of less stickers in the first box and third box than the second box
= (3 u + 120) - (1 u + 40 + 1 u)
= (3 u + 120) - (2 u + 40)
= 3 u - 2 u  + 120 - 40
= 1 u + 80
= 1 x 4 + 80
= 4 + 80
= 84

Answer(s): 84