Let S be the point where the station is located.

The distance SA + SB will be minimized.

If the station is x units away from the west end, then it will be 200 - x units away from the east end.

Use the right triangles:

SA^2 = x^2 + 90^2

SB^2 = ( 200-x)^2 + 60^2

Solve for SA and SB above, respectively, then add both sides to get total length SA + SB = L(x)

Optimize L(x) = using calculus.

I hope this helps. Good luck!