Positive integers a and b are such that the graphs of y=a x+5 and y=3 x+b intersect the x-axis at the same point. What is the sum of all possible x coordinates of these points of intersection?

**Answer Choices**

A. -20

B. -18

C. -15

D. -12

E. -8

Positive integers a and b are such that the graphs of y=a x+5 and y=3 x+b intersect the x-axis at the same point. What is the sum of all possible x coordinates of these points of intersection?

**Answer Choices**

A. -20

B. -18

C. -15

D. -12

E. -8