Adam pays $28.10 for a marble, a bead and a sticker.
The marble costs $3.10 less than the bead.
The bead costs $1.20 less than the sticker.
What is the cost of 8 stickers more than 7 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 3.10
Cost of the sticker = 1 u + 3.10 + 1.20 = 1 u + 4.30

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.10 + 1 u + 4.30
= 3 u + 7.40

3 u + 7.40 = 28.10
3 u = 28.10 - 7.40
3 u = 20.70

1 u = 20.70 ÷ 3 = 6.90

Cost of 8 stickers more than 7 marbles
= 8 x (1 u + 4.30) - 7 x 1 u
= 8 u + 34.40 - 7 u
= 1 u + 34.40
= 1 x 6.90 + 34.40
= 6.90 + 34.40
= $41.30

Answer(s): $41.30