#### Answer

(a) $f = 1.0\times 10^{10}~Hz$
(b) $t = 1.7\times 10^{-4}~s$

#### Work Step by Step

(a) We can find the frequency of microwave radiation with a wavelength of 3.0 cm.
$f = \frac{v}{\lambda}$
$f = \frac{3.0\times 10^8~m/s}{0.030~m}$
$f = 1.0\times 10^{10}~Hz$
(b) We can find the time it takes the signal to travel from one mountaintop to the other.
$t = \frac{d}{v}$
$t = \frac{5.0\times 10^4~m}{3.0\times 10^8~m/s}$
$t = 1.7\times 10^{-4}~s$