Adam pays $17.30 for a marble, a bead and a sticker.
The marble costs $2.50 less than the bead.
The bead costs $1.20 less than the sticker.
What is the cost of 4 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 + 2.50
Cost of the sticker = 1 u + 2.50 + 1.20 = 1 u + 3.70

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.50 + 1 u + 3.70
= 3 u + 6.20

3 u + 6.20 = 17.30
3 u = 17.30 - 6.20
3 u = 11.10

1 u = 11.10 ÷ 3 = 3.70

Cost of 4 marbles less than 5 stickers 
= 5 x (1 u + 3.70) - 4 x 1 u
= 5 u + 18.50 - 4 u
= 1 u + 18.50
= 1 x 3.70 + 18.50
= 3.70 + 18.50
= $22.20

Answer(s): $22.20