First you need to add all the fractions you know. 3/12 + 1/12 = 4/12. Then you subtract your answer of 4/12 to 1/2. But you first need a common denominator. A common factor is 12 for example. 4/12 stays the same, but 1/2 becomes 6/12. 6/12, or 1/2 minus 4/12 is 2/12. Your answer is 2/12 or B.
