Question 960347
c, how many acres of corn;
t, how many acres of tomatos.


Limit on how many planted acres is up to 20 acres.
{{{c+t=20}}}.
Maybe this should really be, {{{c+t<=20}}}.


Janet likes corn.
{{{c>=2t}}}, according to the description part.


{{{t>=5}}}, what Eric wants.


The description really does not give equations, but instead, inequalities.  They are all linear inequalities.  You could have chosen x and y for the acres of each plant; but my choice was c and t, for better telling what each variable means.  You did not ask to solve for how much acreage of tomatos and corn, but only wanted the system.  That as a summary is this:
{{{system(c+t<=20,c>=2t,t>=5)}}}.


You could graph this on a cartesian system and find a <b>region of points</b> satisfying the system.