Step 1: Use the middle of the year as the average date:
If no dates are given, the drawings are assumed to fall evenly through the year, so on average they are taken out in the middle of the year.
Step 2: Count the months from the average date to the year end:
From the middle of the year to the closing date is 6 months, so interest on the total drawings is calculated for 6 months.
Final Answer:
(B) 6 months.