the picture in the attached figure
Let
h-------> the planes height above ground level at the time of the bird strike
we know that
sin 7.7°=opposite side angle 7.7°/hypotenuse
where
opposite side angle 7.7°=h
hypotenuse=4 miles
so
sin 7.7°=h/4-------> h=4*sin 7.7°-----> h=0.54 miles
1 mile-----------> 5280 ft
0.54 mile------> x
x=0.54*5280-----> x=2829.79 ft------> 2830 ft
the answer is
2830 ft
