Adam pays $20.90 for a marble, a bead and a sticker.
The marble costs $3.80 less than the bead.
The bead costs $1.90 less than the sticker.
What is the cost of 5 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 + 3.80
Cost of the sticker = 1 u + 3.80 + 1.90 = 1 u + 5.70

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.80 + 1 u + 5.70
= 3 u + 9.50

3 u + 9.50 = 20.90
3 u = 20.90 - 9.50
3 u = 11.40

1 u = 11.40 ÷ 3 = 3.80

Cost of 5 stickers more than 3 marbles
= 5 x (1 u + 5.70) - 3 x 1 u
= 5 u + 28.50 - 3 u
= 2 u + 28.50
= 2 x 3.80 + 28.50
= 7.60 + 28.50
= $36.10

Answer(s): $36.10