Question 774926
Distance = rate x time.<P>
A travels 2.5 * 4.5 = 11.25 miles before B starts.  The distance B has to cover to overtake A is 11.25 miles.<P>
B overtakes A at the difference of their speeds:  7-4.5=2.5 MPH.<P>
11.25 = 2.5*t so t = 11.25/2.5 = 4.5 hours.