The average price for used DVDs at Moe's Movies is given by the equation y = 4x. In this equation, x represents the number of DVDs purchased and y represents the cost in dollars.
Based on the equation, which of the following is a true statement
A. 40 used DVDs cost $10
B. The cost of 30 used DVDs is $120
C. 30 used DVDs cost $34
D. The cost of 60 used DVDs is $30