Using the following system of inequalities find the maximum value of f(x,y) = 3x+9y x≥0 y≥0 3x+2y≤18 6x+7y≤42? Using the following system of inequalities find the maximum value of f(x,y) = 3x + 3y x≥0 y≥0 3x+2y≤18 6x+7y ≤42?