unassigned use of variable

Question

Hi all was wondering if anyone can help me. I have an equation with an unknown variable (i'm using the equation to get its value) but i am unsure on how to use it. here is some of the code double acceptableProfit = callValidation.validatePrice(profitTxt.Text); //known double ebay1 = callValidation.validatePrice(ebayCostTxt.Text); //known double bprice = callValidation.validatePrice(boughtPriceTxt.Text); //known double recommendedSPrice; double ebay2 = recommendedSPrice/10; double payPal = (2.4 * recommendedSPrice + 20)/100; //to calculate the recommended sale price acceptableProfit = recommendedSPrice - (ebay1 + bprice + ebay2 + payPal); recommendedSPrice = acceptableProfit + ebay1 + bprice + ebay2 + payPal; but obivously for me to use the variable i must define a value for it