Graphing systems of inequalities
https://www.khanacademy.org/math/algebra2/systems_eq_ineq/systems_inequalities_precalc/v/graphing-systems-of-inequalities-2

Writing constraints for linear programming https://www.khanacademy.org/math/algebra2/systems_eq_ineq/systems_inequalities_precalc/e/modeling-constraints

linear programming problem modeled

1. www.youtube.com/watch?v=M4K6HYLHREQhttps
2. www.youtube.com/watch?v=2ACJ9ewUC6Uhttps
3. www.youtube.com/watch?v=I7brzjFhYEU