How to do this question?

Bob owns and manages B Co although he does not keep detailed accounting records. All of Bob’s sales are for cash. He pays certain expenses from his till and then banks the remaining funds. Bob maintains a $1,000 float and operates with a margin of 20%. He has provided you with the following information.
$
Purchases of goods (on credit) 20,000
Wages for clerical assistant (per week; there are 52 weeks in the year) 100
Stationery 500
Electricity 1,200
Bankings 12,800
Opening inventories 2,000
Closing inventories 3,000
Bob is unsure of the level of drawings taken during the year but estimates they were between $60 and $90 per week.
Required What were Bob’s drawings during the year? $