A marble, a bead and a sticker costs $6.70 altogether.
The marble costs $1.20 less than the bead.
The sticker costs $3.10 more than the bead.
How much do 5 stickers cost?
Choose the cheapest item to be 1 u.
The marble costs $1.20 less than the bead.
The cheapest item is the marble.

Cost of the marble = 1 u
Cost of the bead = 1 u + 1.20
Cost of the sticker = 1 u + 1.20 + 3.10 = 1 u + 4.30

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 1.20 + 1 u + 4.30
= 1 u + 1 u + 1 u + 1.20 + 4.30
= 3 u + 5.5

3 u + 5.50 = 6.70
3 u = 6.70 - 5.50
3 u = 1.20

1 u = 1.20 ÷ 3 = 0.40

Cost of 5 stickers
= 5 x (1 u + 4.30)
= 5 x (0.40 + 4.30)
= 5 x 4.70
= $23.50

Answer(s): $23.50