1) You know the height of the bird from the observer is the same as the height of the plane to tower. We also know that the angle of depression is same as the angle of elevation.
So we will use the tangent function to find the value of x.
tan 23 = 5000 / x
x = 5000 / tan 23
x = 11779
You're answer will be 11779 feet
2) We will use the sine function.
sin 35 = 17,000 / x
x = 17,000 / sin 35
x = 29638.6
So the answer would be approximately 29639
