Factorise each expression:
16a=24×a, so factors are 2, 2, 2, 2, a
14ab=2×7×a×b, so factors are 2, 7, a, b
So put together the whole set of factors: 2, 2, 2, 2, 7, a, b (without repeating factors which are common).
Multiply these 112ab. This is the LCM, because 112ab/16a=7b and 112ab/14ab=8, that is, both expressions are factors of the LCM, and the individual divisors have no common factors, so 112ab is the smallest common multiple.