Adam pays $23.20 for a marble, a bead and a sticker.
The marble costs $2.40 less than the bead.
The bead costs $1.30 less than the sticker.
What is the cost of 3 marbles less than 5 stickers?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.40
Cost of the sticker = 1 u + 2.40 + 1.30 = 1 u + 3.70

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.40 + 1 u + 3.70
= 3 u + 6.10

3 u + 6.10 = 23.20
3 u = 23.20 - 6.10
3 u = 17.10

1 u = 17.10 ÷ 3 = 5.70

Cost of 3 marbles less than 5 stickers 
= 5 x (1 u + 3.70) - 3 x 1 u
= 5 u + 18.50 - 3 u
= 2 u + 18.50
= 2 x 5.70 + 18.50
= 11.40 + 18.50
= $29.90

Answer(s): $29.90