The total distance covered by Mary is 6miles total time spent is 2 and half hours average speed is given by,total distance divided by total time so,6/2.5=2.4miles per hour
For the first movie he has 6 choices, then for the second since he has chosen the first there are only 5 left, then for the third there are only 4 choices left and so on.
Therefore the answer is 6!=6*5*4*3*2=720 orderings