Adam pays $27.70 for a marble, a bead and a sticker.
The marble costs $2.60 less than the bead.
The bead costs $1.80 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 + 2.60
Cost of the sticker = 1 u + 2.60 + 1.80 = 1 u + 4.40

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.60 + 1 u + 4.40
= 3 u + 7.00

3 u + 7.00 = 27.70
3 u = 27.70 - 7.00
3 u = 20.70

1 u = 20.70 ÷ 3 = 6.90

Cost of 8 stickers more than 7 marbles
= 8 x (1 u + 4.40) - 7 x 1 u
= 8 u + 35.20 - 7 u
= 1 u + 35.20
= 1 x 6.90 + 35.20
= 6.90 + 35.20
= $42.10

Answer(s): $42.10