Which waves can be transmitted more efficiently by an antenna?

If the sum of the heights of transmitting and receiving antennas in the line of sight $(LOS)$ communication is fixed at $160 \, m$,then the maximum range of $LOS$ communication is $.... \, km$. (Take radius of Earth $R = 6400 \, km$)

$A$ carrier signal of frequency $1.5 MHz$ has an amplitude of $50 V$. It is amplitude modulated by a modulating wave of frequency $10 kHz$ with a modulation index of $50 \%$. What are the frequencies of the $LSB$ and $USB$?

The maximum amplitude for an amplitude modulated wave is found to be $12\, V$ while the minimum amplitude is found to be $3\, V$. The modulation index is $0.6\, x$ where $x$ is $....$

The height of a transmitting antenna at the top of a tower is $25 \; m$ and that of the receiving antenna is $49 \; m$. The maximum distance between them for satisfactory communication in $LOS$ (Line of Sight) is $K \sqrt{5} \times 10^{2} \; m$. The value of $K$ is $\dots$ [Assume radius of Earth is $64 \times 10^{5} \; m$] (Calculate up to the nearest integer value).

$A$ speech signal of $3 kHz$ is used to modulate a carrier signal of frequency $1 MHz$,using amplitude modulation. The frequencies of the side bands will be