The Speed of a Vehicle Varies Inversely as the Time $30 \mathrm{mph}$

The speed of a vehicle varies inversely as the time it takes to travel a fixed distance. If a vehicle travels a fixed distance at 10 miles per hour in 60 minutes, how fast must it travel to cover the same distance in 20 minutes?

A) $30 \mathrm{mph}$
B) $\frac{3}{10} \mathrm{mph}$
C) $120 \mathrm{mph}$
D) $\frac{10}{3} \mathrm{mph}$