Answer:
The ballonist is at a height of 3579.91 ft above the ground at 3:30pm.
Step-by-step explanation:
Let's call:
h the height of the ballonist above the ground,
a the distance between the two observers,
the horizontal distance between the first observer and the ballonist
the horizontal distance between the second observer and the ballonist
and
the angles of elevation meassured by each observer
S the area of the triangle formed with the observers and the ballonist
So, the area of a triangle is the length of its base times its height.
(equation 1)
but we can divide the triangle in two right triangles using the height line. So the total area will be equal to the addition of each individual area.
(equation 2)

But we can write
in terms of
, like this:

And for
will be the same:

Replacing in the equation 2:

And replacing in the equation 1:

So, we can replace all the known data in the last equation:

Then, the ballonist is at a height of 3579.91 ft above the ground at 3:30pm.