Let x be the amount of coffee A, in pounds; then the amount of coffee C is 2x pounds, according to the condition, and the amount of coffee B is (50-x-2x) = (50-3x) pounds. The equation for the price of the mixture is= 13.45 dollars, or 15.37*x + 13.21*(50-3x) + 12.76*2x = 50*13.45. Solve it for x. Then calculate the other amounts.