Step 3 Is where mark made his/her error.
so if the problem was 3/5 divided by 5/8, you will need to reciprocal. that means you have to switch 5/8 into 8/5.
3/5 x 8/5
3 x 8 = 24/?
5 x 5 =25.
the fraction would be 24/25.
So mark made his mistake on step 3 because the denominator isn’t a one digit number such as 5. And so it should be changed to 25.