Adam pays $24.80 for a marble, a bead and a sticker.
The marble costs $3.50 less than the bead.
The bead costs $1.60 less than the sticker.
What is the cost of 2 marbles less than 8 stickers?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 3.50
Cost of the sticker = 1 u + 3.50 + 1.60 = 1 u + 5.10

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.50 + 1 u + 5.10
= 3 u + 8.60

3 u + 8.60 = 24.80
3 u = 24.80 - 8.60
3 u = 16.20

1 u = 16.20 ÷ 3 = 5.40

Cost of 2 marbles less than 8 stickers 
= 8 x (1 u + 5.10) - 2 x 1 u
= 8 u + 40.80 - 2 u
= 6 u + 40.80
= 6 x 5.40 + 40.80
= 32.40 + 40.80
= $73.20

Answer(s): $73.20