Consider the following linear programming problem:

Maximize: $20$x$+30$y

x$+$y$<=80$

$6$x$+12$y$<=600$

x$>=0$

Subject to: y$>=0$

This is a special case of a linear programming problem in which $...$

a$.$ there is no feasible solution.

b$.$ there is a redundant constraint.

c$.$ there are multiple optimal solutions.

d$.$ this cannot be solved graphically.

e$.$none of the above