Help with Excel Formula

I have two components, A and B, each containing percentages of two different materials, C & D.  Lets say i have 500 units of A and 500 units of B available.  A contains 30% of C and 0% of D.  B contains 60% of C and 10% of D.  I want the sum of A and B to equal 300 units and I must have the percentages of C and D equal one another.  Is it possible to set up a formula or multiple formulas to achieve a worksheet where i can enter the details of each component and my desired 300 unit (or any random amount i would want) sum will be met and the percentages of C and D will equal one another?