Question 25175
Total duration ar 30mph = 30(5-x) 
Total duration at 50mph = 50x
50x+30(5-x)=220
50x-30x+150=220
20x=70
x=3.5


Total duration at 50mph = 50(5-x)
Total duration at 30mph = 30x
30x+50(5-x)=220
30x+250-50x=220
-20x=-30
x=1.5


Hence for 30mph the duration was for 3.5h and for 50mph the duration was for about 1.5h
Paul.