if you mean the common denominator to
6/8 , 1/2 and 1/4
you';; have to factor the denominator of each fraction
start w the 1st
factors of 8: 1, 2, 4, 8
factors of 2: 1, 2
factors of 4: 1, 2, 4
Greatest common denominator is 2
because they all have it in their factors list