Which of the following is usually the last step in solving a system of nonlinear equations by substitution ?

The manufacturer of a new product developed the following expression to predict the monthly profit, in thousands of dollars, from sales of the productwhen it is sold at a unit price of x dollars.-0.5x^2 + 22x - 224what is represented by the zero(s) of the expression? a. the profit when the unit price is equal to 0b. the unit price(s) when the profit is equal to 0c. the profit when the unit price is greatestd. the unit price(s) when profit is greatest

Solve for x and y: 217x + 131y = 913; 131x + 217y = 827

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?