Recall the formula of maximum distance between transmitting antenna and receiving antenna for satisfactory communication in terms of the radius of the earth and height of antennas, 

$$\begin{gathered} d=\sqrt{2R{h}_1}+\sqrt{2R{h}_2} \\ \Rightarrow d=\sqrt{2\times 6400\times 0.32}+\sqrt{2\times 6400\times 2}\approx 224 \mathrm{km} \end{gathered}$$