2 beads and 1 marble cost $10.80.
1 bead and 2 marbles cost $9.30.

1. Find the cost of 1 bead and 1 marble.
2. Find the cost of 1 marble.
3. Find the cost of 1 bead.
4. Find the cost of 9 beads and 9 marbles.

(a)
2 beads + 1 marble = 10.80 --- (1)
1 bead + 2 marbles = 9.30 --- (2)

(1) + (2)
3 beads + 3 marbles = 10.80 + 9.30
3 beads + 3 marbles = 20.10 --- (3)

(3) _{÷ 3}
3 beads + 3 marbles = 20.10
1 bead + 1 marble = 20.10 ÷ 3 
1 bead + 1 marble = 6.70 --- (4)

Cost of 1 bead and 1 marble = $6.70

(b)
(2) - (4)
(1 bead + 2 marbles) - (1 bead + 1 marble) = 9.30 - 6.70
1 bead - 1 bead + 2 marbles - 1 marble = 2.60
1 marble = 2.60

Cost of 1 marble = $2.60

(c)
Substitute 1 marble = 2.60 into (4).
1 bead + 1 marble = 6.70
1 bead + 2.60 = 6.70
1 bead = 6.70 - 2.60 = 4.10

Cost of 1 bead = $4.10

(d)
(4) _{x 9}
1 bead + 1 marble = 6.70
9 x (1 bead + 1 marble) = 9 x 6.70
9 beads + 9 marbles = 60.30

Cost of 9 beads and 9 marbles = $60.30

Answer(s): (a) $6.70; (b) $2.60; (c) $4.10; (d) $60.30