A sticker, a bead and a marble costs $8.60 altogether.
The sticker costs $2.70 less than the bead.
The marble costs $1.40 more than the bead.
How much do 3 marbles cost?
Choose the cheapest item to be 1 u.
The sticker costs $2.70 less than the bead.
The cheapest item is the sticker.

Cost of the sticker = 1 u
Cost of the bead = 1 u + 2.70
Cost of the marble = 1 u + 2.70 + 1.40 = 1 u + 4.10

Total cost of the sticker, the bead and the marble
= 1 u + 1 u + 2.70 + 1 u + 4.10
= 1 u + 1 u + 1 u + 2.70 + 4.10
= 3 u + 6.8

3 u + 6.80 = 8.60
3 u = 8.60 - 6.80
3 u = 1.80

1 u = 1.80 ÷ 3 = 0.60

Cost of 3 marbles
= 3 x (1 u + 4.10)
= 3 x (0.60 + 4.10)
= 3 x 4.70
= $14.10

Answer(s): $14.10