Answer: It should cost $5
Step-by-step explanation:
First you have 4 hardcover and 2 softcover, so 4x+2y= $24 and for your friend it would be 3x+3y= $21.
You have
(3x+3y)2 = 72
(4x+2y)3 = 42
Then subtract them which is 30 you would divide by 6 since 3x2=6
Which gets you to 5.
The equation is y = (-1/3)x + 3.
