The only thing I need help with is figuring out these equations. :[

Your grandfather has $303,000 to invest. He has decided to invest all of it by purchasing some shares of stock in each of three companies: a lumber company that sells for $25 per share and has an expected growth of 6.5% per year, a fast food company that sells for $30 per share and has an expected growth of 10% per year and a discount clothing chain that sells for $15 per share and has an expected growth of 12% per year. The total cost of the lumber company shares exceeds the total cost of the clothing chain by $15,000. If the total growth of all the tree is $28,425 for the year, how many shares of each did he buy?

My equations are...

Let -

x = lumber / 25 / 6.5%

y = food / 30 / 10%

z = clothing / 15 / 12%

25x+30y+15z = 303,000

.065x+.1y+.12z = 28,425

-x+z = 15,000

Where did I go wrong? Any help would be greatly appreciated.