Find the Minimum Value of the Objective Function and Where $\ge$

Multiple Choice

Find the minimum value of the objective function and where it occurs, subject to the constraints:
Objective function:

Z = x + 4y

Constraints:

X $\ge$ 0
Y $\ge$ 0
X + 4y $\le$ 20
X + y $\le$ 18
2x + 2y $\le$ 21

A) Minimum at (0, 0) : 0
B) Minimum at (0, 5) : 20
C) Minimum at (0, 18) : 72
D) Minimum at $\left( 0 , \frac { 21 } { 2 } \right) : 42$
E) No minimum