Find the value for c for which the system is consistent and dependent.

3x + y = 5
4.5y = c + 9x

Find the minimum value of f(x, y) = y – x + 1 for the polygonal convex set determined by this system of inequalities.
x > 0 y > 0 2x + y< 4

Find the minimum value of f(x, y) = y – x + 1 for the polygonal convex set determined by this system of inequalities.

x > 0 y > 0 2x + y< 4
the answer is -1. please tell me why