Question 1121534
I believe you mean x is the horizontal distance from the first tower 
to a point on the cable (the distance between the two towers is fixed)
To answer the 1st question, find the value of y for x = 6:
y = 0.05(6 - 30)^2 + 6 -> y = 34.8 m
You are correct that the function is symmetric about x = 30, but the function
is a minimum at x = 30.
Thus the other tower is 30 m away at x = 60, so they are 60 m apart.