Adam pays $8.30 for 2 beads and 3 marbles.
A bead costs $2.40 more than 1 marble.
What is the cost of 4 beads and 2 marbles?
Choose the cheaper item to be 1 u.
1 bead costs $2.40 more than 1 marble.
The cheaper item is the marble.

Cost of the marble = 1 u
Cost of the bead = 1 u + 2.40

Cost of 2 beads = 2 x (1 u + 2.40) = 2 u + 4.80
Cost of 3 marbles = 3 u

Total cost of 2 beads and 3 marbles
= 2 u + 4.80 + 3 u
= 2 u + 3 u + 4.80
= 5 u + 4.80

5 u + 4.80 = 8.30
5 u = 8.30 - 4.80
5 u = 3.50

1 u = 3.50 ÷ 5 = 0.70

Cost of 4 beads and 2 marbles
= 4 x (1 u + 2.40) + 2 u
= 4 u + 9.60 + 2 u
= 4 u + 2 u + 9.60
= 6 u + 9.60
= 6 x 0.70 + 9.60
= 4.20 + 9.60
= $13.80

Answer(s): $13.80