Adam pays $16.40 for 3 marbles and 4 beads.
A marble costs $4.30 more than 1 bead.
What is the cost of 4 marbles and 3 beads?
Choose the cheaper item to be 1 u.
1 marble costs $4.30 more than 1 bead.
The cheaper item is the bead.

Cost of the bead = 1 u
Cost of the marble = 1 u + 4.30

Cost of 3 marbles = 3 x (1 u + 4.30) = 3 u + 12.90
Cost of 4 beads = 4 u

Total cost of 3 marbles and 4 beads
= 3 u + 12.90 + 4 u
= 3 u + 4 u + 12.90
= 7 u + 12.90

7 u + 12.90 = 16.40
7 u = 16.40 - 12.90
7 u = 3.50

1 u = 3.50 ÷ 7 = 0.50

Cost of 4 marbles and 3 beads
= 4 x (1 u + 4.30) + 3 u
= 4 u + 17.20 + 3 u
= 4 u + 3 u + 17.20
= 7 u + 17.20
= 7 x 0.50 + 17.20
= 3.50 + 17.20
= $20.70

Answer(s): $20.70