Answer:
[tex]H = 2.1 mile[/tex]
Explanation:
Let the height of the balloon is H
so we will have
[tex]tan\theta_1 = \frac{H}{d}[/tex]
[tex]tan18 = \frac{H}{d}[/tex]
now after a mile post the angle is 21 degree
so we will have
[tex]tan 21 = \frac{H}{d - 1}[/tex]
so we have
[tex]d = \frac{H}{tan18}[/tex]
[tex]d = 3.08 H[/tex]
also we have
[tex]d - 1 = \frac{H}{tan21}[/tex]
[tex]3.08 H - 1 = 2.6 H[/tex]
[tex]H = 2.1 mile[/tex]