Which of the following lines is parallel to x = 7?

a.) 3y = 7
b.) y = 7
c.) x = y
d.) x = 4

For this case we have the following line:
 x = 7
 This line is a vertical line whose slope tends to infinity.
 To find a parallel line, we must find a line whose slope also tends to infinity.
 Therefore, we must look for a vertical line.
 The line that is vertical for this case is given by:
 x = 4
 
 The following line is parallel to x = 7:
 D.) x = 4