A bead, a marble and a sticker costs $8.70 altogether.
The bead costs $1.30 less than the marble.
The sticker costs $2.20 more than the marble.
How much do 3 stickers cost?
Choose the cheapest item to be 1 u.
The bead costs $1.30 less than the marble.
The cheapest item is the bead.

Cost of the bead = 1 u
Cost of the marble = 1 u + 1.30
Cost of the sticker = 1 u + 1.30 + 2.20 = 1 u + 3.50

Total cost of the bead, the marble and the sticker
= 1 u + 1 u + 1.30 + 1 u + 3.50
= 1 u + 1 u + 1 u + 1.30 + 3.50
= 3 u + 4.8

3 u + 4.80 = 8.70
3 u = 8.70 - 4.80
3 u = 3.90

1 u = 3.90 ÷ 3 = 1.30

Cost of 3 stickers
= 3 x (1 u + 3.50)
= 3 x (1.30 + 3.50)
= 3 x 4.80
= $14.40

Answer(s): $14.40