3 beads and 1 sticker cost $7.50.
1 bead and 3 stickers cost $9.70.

1. Find the cost of 1 bead and 1 sticker.
2. Find the cost of 1 sticker.
3. Find the cost of 1 bead.
4. Find the cost of 7 beads and 7 stickers.

(a)
3 beads + 1 sticker = 7.50 --- (1)
1 bead + 3 stickers = 9.70 --- (2)

(1) + (2)
4 beads + 4 stickers = 7.50 + 9.70
4 beads + 4 stickers = 17.20 --- (3)

(3) _{÷ 4}
4 beads + 4 stickers = 17.20
1 bead + 1 sticker = 17.20 ÷ 4
1 bead + 1 sticker = 4.30 --- (4)

(b)
(2) - (4)
(1 bead + 3 stickers) - (1 bead + 1 marble) = 9.70 - 4.30
1 bead - 1 bead + 3 stickers - 1 sticker = 5.40
2 stickers = 5.40
1 sticker = 5.40 ÷ 2 = 2.70

Cost of 1 sticker = $2.70

(c)
Substitute 1 sticker = 2.70 into (4).
1 bead + 1 sticker = 4.30
1 bead + 2.70 = 4.30
1 bead = 4.30 - 2.70 = 1.60

Cost of 1 bead = $1.60

(d)
(4) _{x 7}
1 bead + 1 sticker = 4.30
7 x (1 bead + 1 marble) = 7 x 4.30
7 beads + 7 stickers = 30.10

Cost of 7 beads and 7 stickers = $30.10

Answer(s): (a) $4.30; (b) $2.70; (c) $1.60; (d) $30.10