If the line tangent to the graph of function f at the point (1,7) passes through the point (-2,-2), then f '(1) is: A)-5 B)1 C)3 D)7 E)undefined

I know that the slope of the tangent line is 3 using (y-y)/(x-x)

Also, I'm thinking that I have to use the mean value theorem but i'm not sure how to apply it to this problem