Given the fraction 5/12 and 9/16, the least common denominator can be get by giving the possible common multiples of 12 and 16.
12 = 12, 24, 36, 48, 60, 72, 84, 96, 108, 120
16 = 16, 32, 48, 64, 80, 96, 112, 128, ...
So looking above, the common are 48 and 86 but the smallest is 48.
So the LCD is 48.