Adam pays $28.40 for a marble, a bead and a sticker.
The marble costs $2.20 less than the bead.
The bead costs $1.20 less than the sticker.
What is the cost of 4 marbles less than 8 stickers?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.20
Cost of the sticker = 1 u + 2.20 + 1.20 = 1 u + 3.40

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.20 + 1 u + 3.40
= 3 u + 5.60

3 u + 5.60 = 28.40
3 u = 28.40 - 5.60
3 u = 22.80

1 u = 22.80 ÷ 3 = 7.60

Cost of 4 marbles less than 8 stickers 
= 8 x (1 u + 3.40) - 4 x 1 u
= 8 u + 27.20 - 4 u
= 4 u + 27.20
= 4 x 7.60 + 27.20
= 30.40 + 27.20
= $57.60

Answer(s): $57.60