A company finds that its profits can be modelled with the formula P = 67.2x - 4.2x2, where P is the profit in millions of dollars and x is the...

A company finds that its profits can be modelled with the formula P = 67.2x - 4.2x2, where P is the profit in millions of dollars and x is the production (in thousands of units). At what profit level is the model valid? Hint: Look at the discriminant.