The common denominator would be the biggest value from your fractions or you can make a number where all of the denominators can multiply up to then simplify the problem later
if the denominators were odd and you cant use one of denominators present you can multiply them together then simplify down 4/8 = 1/2 8/16= 8/16 divide it by two since you can and you get 4/8 then it goes by two again 2/4 then 1/2
