An auto dealer pays an average of $$\$ 8750$$ with a standard deviation of $$\$ 1200$$ for used car trade-ins and sells new cars for an average of $$\$ 28,500$$ with a standard deviation of $$\$ 3100 .$$ Assuming independence of trade-in and new car prices for a customer, what is the standard deviation of the revenue the dealer should expect to make if a customer trades in a used car and buys a new one?
(A) $\sqrt{3100+1200}$ dollars
(B) $\sqrt{3100+1200}$ dollars
(C) $\sqrt{3100^{2}+1200^{2}}$ dollars
(D) $\sqrt{3100^{2}+1200^{2}}$ dollars
(E) $3100-1200$ dollars