A marble, a sticker and a bead costs $7.70 altogether.
The marble costs $1.90 less than the sticker.
The bead costs $3.60 more than the sticker.
How much do 4 beads cost?
Choose the cheapest item to be 1 u.
The marble costs $1.90 less than the sticker.
The cheapest item is the marble.

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

Total cost of the marble, the sticker and the bead
= 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 = 7.70
3 u = 7.70 - 7.40
3 u = 0.30

1 u = 0.30 ÷ 3 = 0.10

Cost of 4 beads
= 4 x (1 u + 5.50)
= 4 x (0.10 + 5.50)
= 4 x 5.60
= $22.40

Answer(s): $22.40