Answer:
(d) one and four twelfths
Step-by-step explanation:
As is often the case, you can look at the answer choices, eliminate the unreasonable ones, and you have the correct answer.
Here, you're subtracting 3-something from 4-something. The result will be near 1-something (eliminating choices A and B).
A "common denominator" is a multiple of the denominators in the problem. That means the common denominator will be a multiple of 12 and 6. 12 is already a multiple of 6, so 12 is a reasonable choice for a common denominator. Looking at the (remaining) answer choices, we know that 18 is not a multiple of 12, so cannot be the "common denominator" (eliminates choice C).
The only reasonable answer choice is the correct one:
one and four twelfths
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We can check this logic by actually working the problem. So far, we know that 12 is the common denominator of choice, so ...
(4 8/12) - (3 2/6) = (4 8/12) -(3 4/12) = (4 -3) +(8/12 -4/12) = 1 4/12
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Additional comment
In "real life" you would recognize that both of these fractions can be reduced to thirds, so you have ...
4 2/3 -3 1/3 = 1 1/3
