Answer:
B would be correct.
Explanation:
You have to subtract the 1/3 and 1/4 by the whole pizza (1) otherwise you never had a whole pizza according to your equation. By doing 1-1/3 you solve for the amount left on Monday, and when you subtract 1/4 from the number you just got, you have solved for the total amount left on Tuesday.
1-1/3=2/3
2/3-1/4= 2/3 * 4/4 - 1/4 * 3/3 =
8/12-3/12= 5/12 of a pizza left