Answer
Use the relativistic velocity formula.
Work Step by Step
$$v=\frac{v_{1}+v_{2}}{1+\frac{v_{1}v_{2}}{c^{2}}}$$
Substitute the numbers.
$$v=\frac{0.80c+0.50c}{1+\frac{0.80c0.50c}{c^{2}}}=0.93c$$
Relative to the Earth, the drone moves at 93 percent of the speed of light.