Step 1: Recall the rule for undated drawings:
When the time of withdrawals is not mentioned, the drawings are assumed to be spread evenly over the year, so interest is charged on the total drawings for an average period of 6 months.
Step 2: Check the other options:
5½ months applies when equal amounts are drawn at the end of every month, 6½ months applies when equal amounts are drawn at the beginning of every month, and 12 months would apply only if the whole amount were drawn on the first day of the year.
Final Answer:
Interest is charged for 6 months.