Answer: One DVD is $12 and one book is $1
Step-by-step explanation:
Let the DVD be d and the book be b.
Case 1:
3d + 4b = $40.......(1)
Case 2:
1d + 6b = $18........... (2)
In this equations above, I intend to eliminate variable d, so I'm going to multiply the coefficient of d in (1) to multiply (2)
3 × (1d + 6b = 18)
3d + 18b = 54........ .(3)
Then, subtract (1) from (3)
3d + 18b = 54
- ( 3d + 4b = 40)
3d - 3d + 18b - 4b = 54 - 40
0 + 14b = 14
b = 14/14
b = 1.
Then substitute 1 for b in (2)
1d + 6(1) = 18
d + 6 = 18
d = 18 - 6
d = 12.
(d,b) = (12,1)
