Answer
The average velocity on an outgoing trip is x miles per hour. The average velocity on the return trip is $20$ miles per hour slower, so the average velocity on the return trip is $x-20$ miles per hour. The distance covered in the return trip is $30$ miles, so the time on the return trip is $\frac{30}{x-20}$ hours.
Work Step by Step
Consider the average velocity on the outgoing trip to be x.
The average velocity on the return trip is $20$ miles per hour slower. So, the average velocity on the return trip is $\left( x-20 \right)$.
When the object travels with the speed $v$ and covers a distance $s$ then the time is given by $t=\frac{s}{v}$
The distance covered in the return trip is $30$ miles and the average velocity on the return trip is $\left( x-20 \right)$, so the time taken on return trip is $\frac{30}{x-20}$.
Therefore, the correct fills for the blanks are $x-20$ and $\frac{30}{x-20}$.
