Explanation:

Let the income of A and B is 3x and 4x respectively
Let the expenditure of A and B is 9y and 5y respectively
The saving of A and B is = (3x - 9y) and (4x - 5y) respectively........(i)
Given ,
Income of A = 3 times the expenditure of B
i.e; 3x =
Putting the value of x and y in equation (i)
Saving of A = (3 × 5) − 9 × 1 = 6
Saving of B = (4 × 5) − 5 × 1 = 15
Required ratio = 6 : 15
i.e; 2 : 5
Hence, Option A is correct.