On her way to visit her parents, Keegan drives 480 miles in 6 hours. What is her average rate of speed in miles per hour.

Please help!!

We know that formula to solve for the area of a trapezoid is A=(a+b)/2+h. So, the formula to find the height would be 2*[A/(a+b)]. 
2*[A/(a+b)] Substitute the values for the variables
2*[25/(6+4)] Solve the parentheses
2*(25/10) 
2*2.5=5
The height must be 5.