How long would it take you to get high enough

[Prep Girl]

I'm 185ft but could be up the hill in minutes that's 235ft, 10minute drive puts me 299ft, half hour 385ft ish and chrishall an hour for me then, chilterns are really high almost 900ft? an hour in the other direction.

I'm to tired to do the maths, 100miles in land needs to be so high 250ft ? so if you were only 30-50 miles inland your in big trouble