A marble, a bead and a sticker costs $6.30 altogether.
The marble costs $1.30 less than the bead.
The sticker costs $1.60 more than the bead.
How much do 4 stickers cost?
Choose the cheapest item to be 1 u.
The marble costs $1.30 less than the bead.
The cheapest item is the marble.

Cost of the marble = 1 u
Cost of the bead = 1 u + 1.30
Cost of the sticker = 1 u + 1.30 + 1.60 = 1 u + 2.90

Total cost of the marble, the bead and the sticker
= 1 u + 1 u + 1.30 + 1 u + 2.90
= 1 u + 1 u + 1 u + 1.30 + 2.90
= 3 u + 4.2

3 u + 4.20 = 6.30
3 u = 6.30 - 4.20
3 u = 2.10

1 u = 2.10 ÷ 3 = 0.70

Cost of 4 stickers
= 4 x (1 u + 2.90)
= 4 x (0.70 + 2.90)
= 4 x 3.60
= $14.40

Answer(s): $14.40