Place the origin of the coordinate system at the bridge level, half way between the towers.


Write the parabola equation in vertex form  y = ax^2  (in this form the cable touches the road at the origin of the coordinate system).


You are given that  y = 180 meters at x = 400 meters.

So you substitute these values into the parabola equation


    180 = a*400^2.


From the equation, you find  a =  = 0.001125.


Thus your parabola is  y = 0.001125*x^2.


Now, to answer the problem question, you substitute  x= 300  into the last equation


    y = 0.001125*300^2 = 101.25 meters.      ANSWER