An apple pie uses 4 cups of apples and 3 cups of flour. An apple cobbler uses 2 cups of apples and 3 cups of flour. You have 16 cups of apples and 15 cups of flour. When you sell these at the Farmer’s Market you make $3.00 profit per apple pie and $2.00 profit per apple cobbler. Use linear programming to determine how many apple pies and how many apple cobblers you should make to maximize your profit.

I'm stuck on the "Write any non-negativity constraints on x and y." part I know the inequality to show constraint for apples is 4x+2y

Question

An apple pie uses 4 cups of apples and 3 cups of flour.  An apple cobbler uses 2 cups of apples and 3 cups of flour.  You have 16 cups of apples and 15 cups of flour.  When you sell these at the Farmer’s Market you make $3.00 profit per apple pie and $2.00 profit per apple cobbler.  Use linear programming to determine how many apple pies and how many apple cobblers you should make to maximize your profit.  

I'm stuck on the "Write any non-negativity constraints on x and y." part I know the inequality to show constraint for apples is 4x+2y<= and the flour equation is 3x+3y<=15