Adam pays $22.30 for a marble, a bead and a sticker.
The marble costs $2.40 less than the bead.
The bead costs $1.90 less than the sticker.
What is the cost of 4 marbles less than 7 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 + 1.90 = 1 u + 4.30

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.40 + 1 u + 4.30
= 3 u + 6.70

3 u + 6.70 = 22.30
3 u = 22.30 - 6.70
3 u = 15.60

1 u = 15.60 ÷ 3 = 5.20

Cost of 4 marbles less than 7 stickers 
= 7 x (1 u + 4.30) - 4 x 1 u
= 7 u + 30.10 - 4 u
= 3 u + 30.10
= 3 x 5.20 + 30.10
= 15.60 + 30.10
= $45.70

Answer(s): $45.70