Adam pays $20.60 for a marble, a bead and a sticker.
The marble costs $2.50 less than the bead.
The bead costs $1.20 less than the sticker.
What is the cost of 9 stickers more than 8 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.50
Cost of the sticker = 1 u + 2.50 + 1.20 = 1 u + 3.70

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.50 + 1 u + 3.70
= 3 u + 6.20

3 u + 6.20 = 20.60
3 u = 20.60 - 6.20
3 u = 14.40

1 u = 14.40 ÷ 3 = 4.80

Cost of 9 stickers more than 8 marbles
= 9 x (1 u + 3.70) - 8 x 1 u
= 9 u + 33.30 - 8 u
= 1 u + 33.30
= 1 x 4.80 + 33.30
= 4.80 + 33.30
= $38.10

Answer(s): $38.10