Answer
a. $268s$ or $\approx 4.5 min$
b. $1266s$ or $\approx 21 min$
Work Step by Step
Use the relationship d = vt and solve for the time.
a. When Mars is closest to the Earth, the distance d to use is the difference between the radii of their orbits, $d _{close}=230\times10^{9}m-149.6\times10^{9}m $
$$t=\frac{d}{v}=\frac{ d_{close}}{2.998\times10^8m/s}=268s\approx 4.5 min$$
b. When Mars is farthest from the Earth, the distance d to use is the sum of the radii of their orbits, $d _{far}=230\times10^{9}m+149.6\times10^{9}m $
$$t=\frac{d}{v}=\frac{ d_{far}}{2.998\times10^8m/s}=1266s\approx 21 min$$
