suppose you sell hats for 10 dollars each and sunglasses for 5 dollars each. you know the expected number of hats sold in a day is 10 with standard deviation 1; you know the expected number of sunglasses sold in a day is 20 with standard deviation 2; you know the sale of hats and sunglasses are independent. what is the standard deviation of your revenues in a day? (round to closest dollar)