1. Use the average speed formula:
\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}
2. Plug in the given values:
\text{Average Speed} = \frac{385 \text{ miles}}{7 \text{ hours}}
3. Divide the total distance by the total time to find the average speed:
\text{Average Speed} = \frac{385}{7}
4. Calculate the result:
\text{Average Speed} = 55 \text{ mph}
Finally, the Sanderson family's average speed was 55 \text{ mph}.