Answer:

Part A is 1/4 of the whole

Part B is 3/4 of the whole

Solution:

Assuming there are no other parts,

the Whole = A + B is the denominator:

Whole = 3 + 9 = 12

Part A = 3 and Part B = 9 are numerators for each fraction.

The fractions are then:

3/12 and 9/12

Meaning:

Part A is 3/12 of the whole

Part B is 9/12 of the whole

Reducing the fractions, it is also true that:

Part A = 1/4 of the whole

Part B = 3/4 of the whole