you look to see the change in the numerator or denominator and apply that to the part of the fraction you are looking for
for example 1/4=?/8
8/4 = 2
that means i have to multiply 2 times 1 to find the value of the numerator
the final answer is 1/4=2/8
6/4=12/?
12/6 = 2
4 times 2 = 8
the answer is 6/4=12/8