How do i do this? what’s the answer?

F(x) = 5x

for f(7) you replace x with 7 so it will be : f(7) = 5(7) = 35

C. as you can see, the small triangle in the larger figure takes up two blocks, while the small triangle in the small figure takes up only one. you are left with a and c. 

a 90 degree rotation doesn't make sense because the triangles will be facing east and southeast.