Question 885773
Distance = Rate x Time 

From Palm Beach to Washington:
900 miles = 450 MPH x Time
900/450 = 2 hrs

From Washington back to Pam Beach:
900 miles = 300 MPH x Time
900/300  = 3 hrs

Total distance = 1800 miles (900 x 2)
Total time = 5 hours  (2 hrs there, 3 hrs back)

So... 

1800/5 = 360 MPH