Question 1154217
.
<pre>

The semiaxes are 170/2 = 85 ft  and  40/2 = 20 ft.


The equation of the ellipse is


    {{{x^2/85^2}}} + {{{y^2/20^2}}} = 1.


From the equation,  


    y = +/- {{{20*sqrt(1 - x^2/85^2)}}}.


Substitute here  x = 85-10 = 75. Then


    y = +/- {{{20*sqrt(1-(75/85)^2)}}} = +/- 9.412  (rounded to 3 decimal places).


So, the answer to the problem's question is  9.412 - (-9.412) = 2*9.412 = 18.824 ft  (rounded).    <U>ANSWER</U>
</pre>

Solved.