Question 765905
The spot where the tower meets the ground is a right angle.  Standing yourself at 100 feet away, this is a leg of the right triangle.  You do not know the distance from yourself to the top of the tower, but you do not need it.  You want the other leg.  The two legs of the right triangle have this relationship, using h as the height of the tower:

{{{tan(40)=h/100}}}
Multiply left and right by 100,
{{{highlight(100*tan(40)=h)}}}.


83.9 feet, almost 84 feet.