Final answer:
The equation relating miles traveled (y) and number of hours (x) for the Smith family's trip is y = 65x, indicating they travel at a constant speed of 65 miles per hour.
Step-by-step explanation:
The question asks for an equation that relates the miles traveled (y) to the number of hours (x) for the Smith family's road trip.
Since they traveled 390 miles in 6 hours, we can calculate their average speed by dividing the total distance by the total time, giving us 390 miles ÷ 6 hours = 65 miles per hour.
This average speed is constant, so the relationship between y and x is linear and can be represented by the equation y = 65x, where y represents the total miles traveled and x represents the number of hours traveled.