Adam pays $18.60 for a marble, a bead and a sticker.
The marble costs $2.10 less than the bead.
The bead costs $1.50 less than the sticker.
What is the cost of 7 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 + 2.10
Cost of the sticker = 1 u + 2.10 + 1.50 = 1 u + 3.60

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.10 + 1 u + 3.60
= 3 u + 5.70

3 u + 5.70 = 18.60
3 u = 18.60 - 5.70
3 u = 12.90

1 u = 12.90 ÷ 3 = 4.30

Cost of 7 stickers more than 5 marbles
= 7 x (1 u + 3.60) - 5 x 1 u
= 7 u + 25.20 - 5 u
= 2 u + 25.20
= 2 x 4.30 + 25.20
= 8.60 + 25.20
= $33.80

Answer(s): $33.80