To find the common ratio in a geometric sequence you have to divide two of its numbers:
For example if you divide 4 by the previous number in the sequence 16/3:
4/ (16/3)= 3/4
If you divide 3 by the previous number in the sequence 4 it equals 3/4.
Remember a geometrical sequence is found by multiplying the previous value by a constant. In this case the constant is 3/4