Answer:
12
Step-by-step explanation:
The least common denominator of the fractions is the least common multiple of the denominators.
Multiples of 3: 3, 6, 9, 12, 15, 18, ...
Multiples of 4: 4, 8, 12, 16, 20, 24, ...
The lowest multiple that is common to 3 and 4 is 12.
LCD of 1/3 and 3/4 is 12.
