Graph the system: $$\left\{ \begin{array}{r@{\,}r@{\,}r} x & \ge & 0 \cr y & \ge & 0 \cr y & \le & 4 \cr 4 x +1 y & \le & 28 \end{array} \right.$$ List the vertices of the region clockwise starting with (0,0):
(0,0); $\ $ (, ); $\ $ (, ); $\ $ (, ).