A sticker, a marble and a bead costs $6.30 altogether.
The sticker costs $1.20 less than the marble.
The bead costs $2.10 more than the marble.
How much do 5 beads cost?
Choose the cheapest item to be 1 u.
The sticker costs $1.20 less than the marble.
The cheapest item is the sticker.

Cost of the sticker = 1 u
Cost of the marble = 1 u + 1.20
Cost of the bead = 1 u + 1.20 + 2.10 = 1 u + 3.30

Total cost of the sticker, the marble and the bead
= 1 u + 1 u + 1.20 + 1 u + 3.30
= 1 u + 1 u + 1 u + 1.20 + 3.30
= 3 u + 4.5

3 u + 4.50 = 6.30
3 u = 6.30 - 4.50
3 u = 1.80

1 u = 1.80 ÷ 3 = 0.60

Cost of 5 beads
= 5 x (1 u + 3.30)
= 5 x (0.60 + 3.30)
= 5 x 3.90
= $19.50

Answer(s): $19.50