Each piglet in a litter is fed exactly one-half pound of a

I possibly found my error and edited my answer. IMO C

Although C is the OA, you didn't give the total number of piglets. According to your variables, X and Y are the amounts of oat and barely respectively, but they are NOT the number of piglets. So what's the number of piglets?

Sorry I forgot.
6kg of total feed; since each piglet is give 0.5kg the total number should be 6/0.5 = 12

but then for some reason, the explanation says that the number of piglets should be 5??? here's how:

We know that each piglet is fed \(1/2\) pound of oats and barely, so each piglet receives either an above average amount of oats and a below average amount of barely, vice versa, or even an average amount of both grains. Neither (1) nor (2) is sufficient by itself, but together, we see that piglet A got a larger share of that oats and a below average amount of barely. (1) tells us that there are more than 4 piglets and (2) tells us that there are fewer than 6 piglets. Thus there are \(5\) piglets.

More mathematically, suppose there are x piglets sharing a total of B pounds of barely and O pounds of oats. Each piglet then receives \((B+O)/x\) pounds of grain. Piglet A received received \(O/4 + B/6\) pounds of grain.

Therefore, \((B+O)/x = (3O+2B)/12\) and \(x/(B+O) = 12/(3O+2B)\)