The answer is B, 2/21. To find the answer for this, you first have to find a common denominator between 2/3 and 4/7. Typically, multiplying each fraction by the denominator of the other fraction will help find the number. In this case, for example, I took 2/3 and multiplied it by 7. As well as taking 4/7 and multiplying it by 3. The answers of this two multiplications are 14/21 and 12/21. By subtracting the 12/21 and the 14/21, you get the final answer of 2/21.