The profit function for a product is given by P(x)=-x^3+9x^2+100x-500, where x is the number of units produced and sold and P is in hundreds of dollars. Use factoring by grouping to find the numbers of units that will give a profit of $40,000. The number of units that will give a profit of $40,000 are . (Type an integer or a fraction. Use a comma to separate answers as needed.)