At a Given Point Above Earth's Surface, the Acceleration Due $7.8 \mathrm {~m} / \mathrm { s } ^ { 2 }$

At a given point above Earth's surface, the acceleration due to gravity is equal to $7.8 \mathrm {~m} / \mathrm { s } ^ { 2 }$
the altitude of this point above Earth's surface? $\left( G = 6.67 \times 10 ^ { - 11 } \mathrm {~N} \cdot \mathrm { m } ^ { 2 } / \mathrm { kg } ^ { 2 } , M _ { \text {earth } } = 5.97 \times 10 ^ { 24 } \right.$ $\mathrm { kg } , R _ { \text {earth } } = 6.38 \times 10 ^ { 6 } \mathrm {~m} \text { ) }$

A) 1500 km
B) 770 km
C) 2000 km
D) 2400 km
E) 970 km