Find the minimum and maximum of the function $z = 7 x - 4 y$ subject to

$$\left\{\begin{array}{rcr} y & \ge & 1 \cr y & \le & 8 \cr 7 x - 3 y & \ge & -3 \cr 7 x + y & \le & 71 \end{array}\right.$$

What are the corner points of the feasible set?

The minimum is and maximum is . Type "None" in the blank provided if the quantity does not exist.