how do you work out % ?
ie:

49 miles is what should have been driven but it was actually 61 miles so how much, as a % did the driver cover more than he was supposed to?

and the same but covering 81 mils instead of 63

if he shoudl have done 100 and did 150 he did 50% more than he should
have done

it's monday and i'm getting it wrong