Not going to give the answer, but here's how you get it.
(1) Find the lowest common denominator for 3 and 7 which is 21 (in this case multiplying 3x7 gives you the lowest common denominator)
(2) Convert each of the two fractions so they are expressed with that common denominator. For 4/3 you multiply both the numerator and the denominator by 7 to get 28/21. For 5/7 you multiply both by 3 to get 15/21. Now the equation is 28/21 x 15/21.
(3) Multiply the numerators (28 x 15 = N) and denominators (21 x 21 = D)
