2/7 cup of flour
Simply multiply 2/3 by 3/7 to get the answer. To multiply 2 fractions together, you multiply the numerators together and then multiply the denominator together.
2/3 x 3/7 = 6/21
But 6/21 can be expressed in a simpler fashion. Notice that both 6 and 21 can be evenly divided by 3. So divide both the numerator and denominator by 3
(6/3)/(21/3) = (2)/(7) = 2/7