Adam pays $28.50 for a marble, a bead and a sticker.
The marble costs $2.80 less than the bead.
The bead costs $1.60 less than the sticker.
What is the cost of 4 stickers more than 3 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.80
Cost of the sticker = 1 u + 2.80 + 1.60 = 1 u + 4.40

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.80 + 1 u + 4.40
= 3 u + 7.20

3 u + 7.20 = 28.50
3 u = 28.50 - 7.20
3 u = 21.30

1 u = 21.30 ÷ 3 = 7.10

Cost of 4 stickers more than 3 marbles
= 4 x (1 u + 4.40) - 3 x 1 u
= 4 u + 17.60 - 3 u
= 1 u + 17.60
= 1 x 7.10 + 17.60
= 7.10 + 17.60
= $24.70

Answer(s): $24.70