Adam pays $20.80 for a marble, a bead and a sticker.
The marble costs $3.30 less than the bead.
The bead costs $1.30 less than the sticker.
What is the cost of 7 stickers more than 2 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 3.30
Cost of the sticker = 1 u + 3.30 + 1.30 = 1 u + 4.60

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.30 + 1 u + 4.60
= 3 u + 7.90

3 u + 7.90 = 20.80
3 u = 20.80 - 7.90
3 u = 12.90

1 u = 12.90 ÷ 3 = 4.30

Cost of 7 stickers more than 2 marbles
= 7 x (1 u + 4.60) - 2 x 1 u
= 7 u + 32.20 - 2 u
= 5 u + 32.20
= 5 x 4.30 + 32.20
= 21.50 + 32.20
= $53.70

Answer(s): $53.70