So, the question’s a bit weird, but I’m going to assume it’s asking for what fraction of her walk she had completed:
Basically you need to divide 3/5 by 4/5
Dividing a fraction is the same as multiplying as the reciprocal of the fraction (the top and bottom get reversed)
Therefore you need to find 3/5 • 5/4
Solving this should get you 15/20, which can be simplified to 3/4.
So the answer is she has completed 3/4 of her walk (75%)