Compute the approximate acceleration of gravity for an object above the earth's surface, assigning accel_gravity with the result. The expression for the acceleration of gravity is: (G*M)/(d2), where G is the gravitational constant 6.673 x 10-11, M is the mass of
the earth 5.98 x 1024 (in kg), and d is the distance in meters from the Earth's center (stored in variable dist_center)
Sample output with input: 6.3782e6 (100 m above the Earth's surface at the equator)
Acceleration of gravity: 9.81