Adam pays $21.40 for a marble, a bead and a sticker.
The marble costs $2.70 less than the bead.
The bead costs $1.60 less than the sticker.
What is the cost of 9 stickers more than 3 marbles?
Choose the cheapest item to be 1 u.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.70
Cost of the sticker = 1 u + 2.70 + 1.60 = 1 u + 4.30

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 2.70 + 1 u + 4.30
= 3 u + 7.00

3 u + 7.00 = 21.40
3 u = 21.40 - 7.00
3 u = 14.40

1 u = 14.40 ÷ 3 = 4.80

Cost of 9 stickers more than 3 marbles
= 9 x (1 u + 4.30) - 3 x 1 u
= 9 u + 38.70 - 3 u
= 6 u + 38.70
= 6 x 4.80 + 38.70
= 28.80 + 38.70
= $67.50

Answer(s): $67.50