Simple excel model

Create a simple excel financial model where I have the following The product is financing. A pool of money (dynamic field) Product X Product Y Rate for product X (dynamic field) Rate for Product Y (dynamic field) Price for product X (dynamic field) Price for Product Y (dynamic field) The goal of the model is see how many units of x do I need to sell at a given rate to ensure that I have an average yearly rate for Products x and y of Z % (Z is dynamic). If my pool of money is 50 million dollars, and if I sell 5 x units for 150K USD at 15% then I can lower my rate for product y and will still achieve a yearly yield of 12% for both x and y. The model will tell me (You sold 5 units of X at 150K USD at 15% so you have created for yourself this amount of money to be sold at product Y for a lower rate and you will still achieve a rate of 12% yearly for your pool of money) I need to be able to manipulate the model where I can tinker with Product Y as well by selling it at, for example, 8% which will force me to sell a certain numbers of product X to achieve a yearly return of 12% for my pool of money.