Question 1170273
If draw the described figure, and if not follow the expectation to use Law Of Cos or Law Of Sin but use tangent and its double angle formula instead,


x and 2x the angles of elevations;
h, the tower height


{{{system(h/9=tan(x),h/4=tan(2x))}}}


{{{h/4=(2tan(x))/(1-tan^2(x))}}}

subst. for tan(x):


{{{h/4=(2(h/9))/(1-(h/9)^2)}}}
.
.
{{{highlight(h=3)}}}


(not been rechecked)