Adam pays $21.20 for a marble, a bead and a sticker.
The marble costs $3.60 less than the bead.
The bead costs $1.70 less than the sticker.
What is the cost of 7 stickers more than 4 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 3.60
Cost of the sticker = 1 u + 3.60 + 1.70 = 1 u + 5.30

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.60 + 1 u + 5.30
= 3 u + 8.90

3 u + 8.90 = 21.20
3 u = 21.20 - 8.90
3 u = 12.30

1 u = 12.30 ÷ 3 = 4.10

Cost of 7 stickers more than 4 marbles
= 7 x (1 u + 5.30) - 4 x 1 u
= 7 u + 37.10 - 4 u
= 3 u + 37.10
= 3 x 4.10 + 37.10
= 12.30 + 37.10
= $49.40

Answer(s): $49.40