4 stickers and 1 bead cost $15.80.
1 sticker and 4 beads cost $13.70.

1. Find the cost of 1 sticker and 1 bead.
2. Find the cost of 1 bead.
3. Find the cost of 1 sticker.
4. Find the cost of 9 stickers and 9 beads.

(a)
4 stickers + 1 bead = 15.80 --- (1)
1 sticker + 4 beads = 13.70 --- (2)

(1) + (2)
5 stickers + 5 beads = 15.80 + 13.70
5 stickers + 5 beads = 29.50 --- (3)

(3) _{÷ 5}
5 stickers + 5 beads = 29.50
1 sticker + 1 bead = 29.50 ÷ 5
1 sticker + 1 bead = 5.90 --- (4)

(b)
(2) - (4)
(1 sticker + 4 beads) - (1 sticker + 1 marble) = 13.70 - 5.90
1 sticker - 1 sticker + 4 beads - 1 bead = 7.80
3 beads = 7.80
1 bead = 7.80 ÷ 3 = 2.60

Cost of 1 bead = $2.60

(c)
Substitute 1 bead = 2.60 into (4).
1 sticker + 1 bead = 5.90
1 sticker + 2.60 = 5.90
1 sticker = 5.90 - 2.60 = 3.30

Cost of 1 sticker = $3.30

(d)
(4) _{x 9}
1 sticker + 1 bead = 5.90
9 x (1 sticker + 1 marble) = 9 x 5.90
9 stickers + 9 beads = 53.10

Cost of 9 stickers and 9 beads = $53.10

Answer(s): (a) $5.90; (b) $2.60; (c) $3.30; (d) $53.10