Ok we know that he has a(8lb.)& b(11lb) barrels to fill his hold with 12 barrels(total of 103lb.
So the total of barrels is : a + b = 12 so the third option is wrong and the last one should have subtracted b from 12
The total equation is 8a + 11b = 103. Similarly, they should subtract 11b from 103. So the second is out and A is CORRECT