You have to set it up clearly and cleanly and neatly.
a).
3 and 1/4 = 13/4 = 26/8
2 and 1/2 = 5/2 = 20/8
5/8 = 5/8
Add the eighths: (26 + 20 + 5)/8 = 51/8 = 6 and 3/8
b).
We want to know how many times 1/4 goes into the total amount.
51/8 = 25.5/4
That's 25 full servings, with 1/2 serving left over.
==============================================
For me, this whole thing is much easier if you work it in decimals.
a).
3 and 1/4 = 3.25
2 and 1/2 = 2.50
5/8 = . . . . . 0.625
Add um up: 6.375 quarts
b).
A serving is 0.25 quart.
Divide 6.375 by 0.25 = 25.5 . . . 25 full servings, with 1/2 left for the kitchen help.