Fire insurance - loss of stock

Hi , can any one throw some light on the problem mentioned below:- Sales 350000,Purchases -300000,wages -10000,opening stock is 10000 less then closing stock. Find the gross profit ratio. I am using the formula : Op st. + purchases + wages + gross profit = Sales + closing stock. Assuming closing stock as y and gross profit as x which gives me 14.27%. But when i substitute the value of x in the equation i am not getting proper answer. Please guide me as to whether the modus operandi followed by me is correct.