Adam pays $17.60 for a marble, a bead and a sticker.
The marble costs $2.90 less than the bead.
The bead costs $1.60 less than the sticker.
What is the cost of 4 stickers more than 2 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.90
Cost of the sticker = 1 u + 2.90 + 1.60 = 1 u + 4.50

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.90 + 1 u + 4.50
= 3 u + 7.40

3 u + 7.40 = 17.60
3 u = 17.60 - 7.40
3 u = 10.20

1 u = 10.20 ÷ 3 = 3.40

Cost of 4 stickers more than 2 marbles
= 4 x (1 u + 4.50) - 2 x 1 u
= 4 u + 18.00 - 2 u
= 2 u + 18.00
= 2 x 3.40 + 18.00
= 6.80 + 18.00
= $24.80

Answer(s): $24.80