Adam pays $21.60 for a marble, a bead and a sticker.
The marble costs $3.50 less than the bead.
The bead costs $1.10 less than the sticker.
What is the cost of 2 marbles less than 6 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 + 1.10 = 1 u + 4.60

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 3.50 + 1 u + 4.60
= 3 u + 8.10

3 u + 8.10 = 21.60
3 u = 21.60 - 8.10
3 u = 13.50

1 u = 13.50 ÷ 3 = 4.50

Cost of 2 marbles less than 6 stickers 
= 6 x (1 u + 4.60) - 2 x 1 u
= 6 u + 27.60 - 2 u
= 4 u + 27.60
= 4 x 4.50 + 27.60
= 18.00 + 27.60
= $45.60

Answer(s): $45.60