A transmitting antenna at top of a tower has a height of

$\mathrm{d}_{\mathrm{t}}=\sqrt{2 \mathrm{Rh}_{1}}+\sqrt{2 \mathrm{Rh}_{2}}$

$=\sqrt{2 \mathrm{R}}\left(\sqrt{\mathrm{h}_{1}}+\sqrt{\mathrm{h}_{2}}\right)$

$=\left(2 \times 6400 \times 10^{3}\right)^{1 / 2}(\sqrt{50}+\sqrt{80})$

$=3578(7.07+8.94)$

$=57.28 \mathrm{Km}$