A gardener has two fertilisers that contain different concentrations of nitrogen. One is 3% nitrogen and the other is 11% nitrogen. How many pounds of each should she mix to obtain 20 pounds of a 9% concentration? 1. Define the variables if they are not already defined in the problem, i. e. Let x be and y be (10 marks).

2. How many equations do we need to model the problem? Write down the equations in terms of the variables (20 marks)

3. Solve the system of equations by substitution or elimination. Write down the steps clearly (20 marks).

4. Sketch the graph of this system of equations. Indicate the x-intercept and y-intercept of each equation. Also indicate the intersection point (40 marks).

5. Indicate the solution and make a recommendation to the gardener(10 marks).