Write the pair of fractions as a pair of fractions with a common denominator 1/3 and 3/4

1/3 and 3/4

for 1/3: multiply top and bottom by 4, which will be 4/12

for 3/4: multiply top and bottom by 3, which will be 9/12

Now both fractions have the same denominator.

1/3 will become 4/12

3/4 will become 9/12