A bead, a marble and a sticker costs $9.80 altogether.
The bead costs $1.90 less than the marble.
The sticker costs $3.60 more than the marble.
How much do 3 stickers cost?
Choose the cheapest item to be 1 u.
The bead costs $1.90 less than the marble.
The cheapest item is the bead.

Cost of the bead = 1 u
Cost of the marble = 1 u + 1.90
Cost of the sticker = 1 u + 1.90 + 3.60 = 1 u + 5.50

Total cost of the bead, the marble and the sticker
= 1 u + 1 u + 1.90 + 1 u + 5.50
= 1 u + 1 u + 1 u + 1.90 + 5.50
= 3 u + 7.4

3 u + 7.40 = 9.80
3 u = 9.80 - 7.40
3 u = 2.40

1 u = 2.40 ÷ 3 = 0.80

Cost of 3 stickers
= 3 x (1 u + 5.50)
= 3 x (0.80 + 5.50)
= 3 x 6.30
= $18.90

Answer(s): $18.90