Question 1144200
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<pre>

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


    {{{(15.37*x + 13.21*(50-3x) + 12.76*(2x))/50}}} = 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.
</pre>

I reduced your problem for you to one single equation for one unknown.


The rest is a simple arithmetic.