A marble, a bead and a sticker costs $9.10 altogether.
The marble costs $1.90 less than the bead.
The sticker costs $3.80 more than the bead.
How much do 4 stickers cost?
Choose the cheapest item to be 1 u.
The marble costs $1.90 less than the bead.
The cheapest item is the marble.

Cost of the marble = 1 u
Cost of the bead = 1 u + 1.90
Cost of the sticker = 1 u + 1.90 + 3.80 = 1 u + 5.70

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 1.90 + 1 u + 5.70
= 1 u + 1 u + 1 u + 1.90 + 5.70
= 3 u + 7.6

3 u + 7.60 = 9.10
3 u = 9.10 - 7.60
3 u = 1.50

1 u = 1.50 ÷ 3 = 0.50

Cost of 4 stickers
= 4 x (1 u + 5.70)
= 4 x (0.50 + 5.70)
= 4 x 6.20
= $24.80

Answer(s): $24.80