Adam pays $22.90 for a marble, a bead and a sticker.
The marble costs $2.90 less than the bead.
The bead costs $1.20 less than the sticker.
What is the cost of 8 stickers more than 6 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 + 1.20 = 1 u + 4.10

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.90 + 1 u + 4.10
= 3 u + 7.00

3 u + 7.00 = 22.90
3 u = 22.90 - 7.00
3 u = 15.90

1 u = 15.90 ÷ 3 = 5.30

Cost of 8 stickers more than 6 marbles
= 8 x (1 u + 4.10) - 6 x 1 u
= 8 u + 32.80 - 6 u
= 2 u + 32.80
= 2 x 5.30 + 32.80
= 10.60 + 32.80
= $43.40

Answer(s): $43.40