Well if she can grade 25 in 4 hours..
First we have to find out how many she can grade in 1 hour
to find that out you can just divide the papers/hours= the paper per 1 hour
25/4= 6.25 papers per hour
So then to figure out how many papers the teacher can grade in 6 hours you multiply the number of papers per hour x the number of hours= number of papers in 6 hours
6.25*6= 37.5 papers in 6 hours
so the answer would be A) 37.5