I'd solve this by the following steps:
1/4 is less than 5/12 (because 1/4 is 3/12), so just as you would borrow for non-fraction subtraction, you can sort of borrow here by turning 8 1/4 into 7 + 1 1/4. Then:
(7 + 1 1/4) - (3 5/12)
= (7 - 3) + (1 1/4 - 5/12)
= 4 + (1 1/4 - 5/12)
To solve the fractional part, convert to non-mixed numbers, then find the least common multiple.
1 1/4 - 5/12
= 4/4 + 1/4 - 5/12
= 5/4 - 5/12
The least common multiple of 4 and 12 is 12, so:
= 15/12 - 5/12
Subtract the numerators and then simplify if you can:
= 10/12
= 5/6
So Wendy has 4 5/6 pounds of carrots left.
