First, find the value of m. You are told that 3m is 81. Well, 81 is 9 × 9 and 9 is 32. So you have 32×32 = 81 or 3 × 3 × 3 × 3 = 81. There are four factors of 3in 81, so m has the value 4. Now 43 is 4 × 4 × 4 is 64. So (D) is correct. Note that (A) is a trap—that’s the value of m, not m3.