A bead, a sticker and a marble costs $9.50 altogether.
The bead costs $2.70 less than the sticker.
The marble costs $3.20 more than the sticker.
How much do 2 marbles cost?
Choose the cheapest item to be 1 u.
The bead costs $2.70 less than the sticker.
The cheapest item is the bead.

Cost of the bead = 1 u
Cost of the sticker = 1 u + 2.70
Cost of the marble = 1 u + 2.70 + 3.20 = 1 u + 5.90

Total cost of the bead, the sticker and the marble
= 1 u + 1 u + 2.70 + 1 u + 5.90
= 1 u + 1 u + 1 u + 2.70 + 5.90
= 3 u + 8.6

3 u + 8.60 = 9.50
3 u = 9.50 - 8.60
3 u = 0.90

1 u = 0.90 ÷ 3 = 0.30

Cost of 2 marbles
= 2 x (1 u + 5.90)
= 2 x (0.30 + 5.90)
= 2 x 6.20
= $12.40

Answer(s): $12.40