Hardrock, a fine craft brewer, sells two brands of beers: T and D. Over the past several years, annual sales volumes of T have averaged 8,000 bottles with a standard deviation of 400 bottles, while annual sales volumes of D have averaged 1,000 bottles with a standard deviation of 300 bottles. The correlation between the sales volumes of the two brands is 0.4. T sells for $2.00 per bottle while D sells for $3.00 per bottle.
Let T and D denote the annual sales volumes for T and D respectively.
(a) What is the standard deviation of Hardrock's annual revenue from D? $___________