Adam pays $29.80 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 9 stickers more than 3 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 = 29.80
3 u = 29.80 - 7.00
3 u = 22.80

1 u = 22.80 ÷ 3 = 7.60

Cost of 9 stickers more than 3 marbles
= 9 x (1 u + 4.40) - 3 x 1 u
= 9 u + 39.60 - 3 u
= 6 u + 39.60
= 6 x 7.60 + 39.60
= 45.60 + 39.60
= $85.20

Answer(s): $85.20