Question 868331
Use Law of Cosines...


A picture will help but is <b>not</b> here included.


Pick the interior angle at the vertex of the 20 m and 30 m sides. Call the angle measure, t.
{{{20^2+30^2-2*20*30*cos(t)=25^2}}}
.
{{{1300-625=1200cos(t)}}}
{{{cos(t)=675/1200}}}
{{{cos(t)=9/16}}}
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What is this value of t?
{{{arcos(9/16)=55.7711}}} degrees for more accuracy than needed.


Use the 20 meter length side as the hypotenuse of a right triangle which contains the altitude and part of the base side; we do not need the base side nor part of it here.  We only want to compute the altitude.  This altitude is:

{{{highlight(highlight(20*sin(55.7711)))}}}.
16.5 meters.