Final answer:
David must walk an additional 5/12 mile to get to the school.
Step-by-step explanation:
To calculate how much further David must walk to get to the school, we need to subtract the distance he has already walked from the total distance to the school.
David has already walked 1/3 of a mile.
The school is 3/4 of a mile from his home.
To find out how much further David must walk, we subtract 1/3 from 3/4:
3/4 - 1/3 = 9/12 - 4/12 = 5/12
So, David must walk 5/12 mile further to get to the school.