A bead, a sticker and a marble costs $7.20 altogether.
The bead costs $1.10 less than the sticker.
The marble costs $1.40 more than the sticker.
How much do 5 marbles cost?
Choose the cheapest item to be 1 u.
The bead costs $1.10 less than the sticker.
The cheapest item is the bead.

Cost of the bead = 1 u
Cost of the sticker = 1 u + 1.10
Cost of the marble = 1 u + 1.10 + 1.40 = 1 u + 2.50

Total cost of the bead, the sticker and the marble
= 1 u + 1 u + 1.10 + 1 u + 2.50
= 1 u + 1 u + 1 u + 1.10 + 2.50
= 3 u + 3.6

3 u + 3.60 = 7.20
3 u = 7.20 - 3.60
3 u = 3.60

1 u = 3.60 ÷ 3 = 1.20

Cost of 5 marbles
= 5 x (1 u + 2.50)
= 5 x (1.20 + 2.50)
= 5 x 3.70
= $18.50

Answer(s): $18.50