The Least Common Multiple (L.C.M.) of two or more integers is the smallest positive integer that is divisible by each of the numbers. To find the L.C.M., we can use the prime factorization method or the listing multiples method. For example, for the pair (64, 84), the prime factorization of 64 is 2^6 and for 84 it is 2^2 * 3^1 * 7^1. The L.C.M. is found by taking the highest power of each prime that appears in the factorizations, which results in L.C.M. = 2^6 * 3^1 * 7^1 = 672. Similarly, for the other pairs, we can calculate their L.C.M.s as shown in the answers.