Adam pays $29.40 for a marble, a bead and a sticker.
The marble costs $2.10 less than the bead.
The bead costs $1.80 less than the sticker.
What is the cost of 8 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 + 2.10
Cost of the sticker = 1 u + 2.10 + 1.80 = 1 u + 3.90

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.10 + 1 u + 3.90
= 3 u + 6.00

3 u + 6.00 = 29.40
3 u = 29.40 - 6.00
3 u = 23.40

1 u = 23.40 ÷ 3 = 7.80

Cost of 8 stickers more than 4 marbles
= 8 x (1 u + 3.90) - 4 x 1 u
= 8 u + 31.20 - 4 u
= 4 u + 31.20
= 4 x 7.80 + 31.20
= 31.20 + 31.20
= $62.40

Answer(s): $62.40