Adam pays $19.80 for 4 stickers and 2 beads.
A sticker costs $3.90 more than 1 bead.
What is the cost of 3 stickers and 2 beads?
Choose the cheaper item to be 1 u.
1 sticker costs $3.90 more than 1 bead.
The cheaper item is the bead.

Cost of the bead = 1 u
Cost of the sticker = 1 u + 3.90

Cost of 4 stickers = 4 x (1 u + 3.90) = 4 u + 15.60
Cost of 2 beads = 2 u

Total cost of 4 stickers and 2 beads
= 4 u + 15.60 + 2 u
= 4 u + 2 u + 15.60
= 6 u + 15.60

6 u + 15.60 = 19.80
6 u = 19.80 - 15.60
6 u = 4.20

1 u = 4.20 ÷ 6 = 0.70

Cost of 3 stickers and 2 beads
= 3 x (1 u + 3.90) + 2 u
= 3 u + 11.70 + 2 u
= 3 u + 2 u + 11.70
= 5 u + 11.70
= 5 x 0.70 + 11.70
= 3.50 + 11.70
= $15.20

Answer(s): $15.20