Answer :

well, let's scope out the scale of the problem, take it step by step... 

First, we need to know the range.:
7 tens is essentially 7 times ten, or 70.
7 tenths is 7/10, or .7
So, subtract .7 from 70 to get the difference of 69.3, which is your answer.
AL2006

Her answer was wrong by a factor of 10² .

That means it was 100 times too large.