Asatellite rotates 50 miles above earth's atmosphere an astronaut works on the satellite and sees the sun rise over the earth to the nearest mile what is the distance from the astronaut to the horizon ? (hint earths radious is about 4000 miles)

A line from the astronaut and tangent to the Earth's surface will be at right angles to a line from the center of the Earth to its surface at the point of tangency.
So, you have a right triangle with one leg of 4000 miles and a hypotenuse of 4050 miles. Determine the other leg. 

4050^2 = 4000^2 + x^2
16,402,500  = 16,000,000
√402500
=634.43m