help in algebra 1

Question

Write a system of equations to model this situation. Then use your system to solve. At a garage sale a CD costs three books and 2 CDs. You spent $18. What is the price of a CD and the price of a book?

Answer 1

 If questions is rewritten saying a CD cost is 3 books. and on 3 books and 2 CD you spent $18. Then we can solve the problem as below.

b = price of books & c= price of cds

3b + 2c = 18 

c = 3b

I am using substitution to solve

3b + 2(3b) = 18    I solved for one variable

3b +6b = 18

9b = 18

b = $2  Cost of the book

c = $6  Cost of the CD