Adam pays $28.50 for a marble, a bead and a sticker.
The marble costs $2.70 less than the bead.
The bead costs $1.50 less than the sticker.
What is the cost of 9 stickers more than 5 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.70
Cost of the sticker = 1 u + 2.70 + 1.50 = 1 u + 4.20

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.70 + 1 u + 4.20
= 3 u + 6.90

3 u + 6.90 = 28.50
3 u = 28.50 - 6.90
3 u = 21.60

1 u = 21.60 ÷ 3 = 7.20

Cost of 9 stickers more than 5 marbles
= 9 x (1 u + 4.20) - 5 x 1 u
= 9 u + 37.80 - 5 u
= 4 u + 37.80
= 4 x 7.20 + 37.80
= 28.80 + 37.80
= $66.60

Answer(s): $66.60