160 stickers are in 3 boxes.
The third box has 3 times as many stickers as the first box.
The second box is 30 less than the first box.
How many less stickers are there in the first box and the second box than in the third box?
Choose the box with the least stickers to be 1 u.

Number of stickers in the second box = 1 u
Number of stickers in the first box = 1 u + 30
Number of stickers in the third box = 3 x (1 u + 30) = 3 u + 90

Total number of stickers
= 3 u + 90 + 1 u + 30 + 1 u
= 3 u + 1 u + 1 u + 90 + 30
= 5 u + 120

5 u + 120 = 160
5 u = 160 - 120
5 u = 40

1 u = 40 ÷ 5 = 8

Number of less stickers in the first box and second box than the third box
= (3 u + 90) - (1 u + 30 + 1 u)
= (3 u + 90) - (2 u + 30)
= 3 u - 2 u  + 90 - 30
= 1 u + 60
= 1 x 8 + 60
= 8 + 60
= 68

Answer(s): 68