Find the Minimum Value of the Objective Function and Where $\left( 0 , \frac { 21 } { 2 } \right) : 42$

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 ? 0
Y ? 0
X + 4y ? 20
X + y ? 18
?2x + 2y ? 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