The picture is in the attachment.
x- horizontal distance between Susan and a bird
7 - x - horizontal distance between Math and a bird;
h / x = tan 20° = 0.364
h / (7 - x) = tan 50°= 1.192
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h = 0.364 x
0.364 x / (7 - x ) = 1.192
0.364 x = 1.192 ( 7 - x )
0.364 x = 8.344 - 1.192 x
1.556 x = 8.344
x = 8.344 : 1.556 = 5.362 km
h = 0.364 · 5.362
h = 1.952 km
.. the bird is at height of
1.952 km from the ground.
