Answer
7.3 kilometers
Work Step by Step
We know that the angle between the plane and where the sound wave following it is:
$\theta = sin^{-1}(\frac{1}{2.2})$
We see how far the sound wave is away:
$d = 2.2 \times 19 \times 340 = 14,212m=14.21 \ km$
This allows us to find the altitude of the plane:
$h = 14.21 \times tan( sin^{-1}(\frac{1}{2.2})) = 7.3 \ km$
