How far above the surface of the earth would you have to be before your weight is reduced by 12.89%? Please Help !

mg = G•m •M/R²

where R = 6.378•10⁶ m,

100%=12.89% =87.11%.

mg₁ =0.8711mg =>
G•m •M/(R+h)² = 0.8711 G•m •M/R²
0.8711(R+h)² = R²
0.8711 (R² +2Rh+h²) = R²
Solve for h