What is the observatory's altitude? Assume R(earth) = 6.37 x 106 m

A sensitive gravimeter at a mountain observatory finds that the free-fall acceleration is 0.0050 m/s2 less than that at sea level (g(sea level) = 9.83 m/s2). What is the observatory’s altitude? Assume R(earth) = 6.37 x 106 m.