At height h above the surface of earth, the gravitational acceleration is what is

The acceleration of gravity is inversely proportional to
the square of the distance from Earth's center.

The acceleration of gravity is 9.8 m/s² on the Earth's surface ...
6380 km from the center.

If the acceleration of gravity at 'h' is 4.9 m/s² ... 1/2 of what it is
on the surface, then the distance from the center is

                 (6380 x √2) =  9,023 km  (rounded) ,

and 'h' is the distance above the surface

                     = (9,023 - 6,380) =  2,643 km  (rounded) .

Here's link to the

cutt.ly/rzNrBcz