Find the distance traveled between the two time readings:

$\text{Distance} = |117 - 97| = 20 \text{ miles}$

The elapsed time is 20 minutes. Convert to hours:

$20 \text{ min} = \frac{20}{60} = \frac{1}{3} \text{ hour}$

Calculate speed:

$\text{Speed} = \frac{20}{1/3} = 20 \times 3 = 60 \text{ mph}$