Question 787508
What we would do is first graph these descriptions onto x y plane:
{{{x<=5}}}, {{{y>=4}}}, {{{-2x+5y<=30}}}.


That will form a planar figure.  You would expect the optimal solution to C to be one of the vertices of this planar figure.  Test each vertex point, and find which one give the maximum and which gives the minimum.


The first two constraints are simple to graph.  The last given constraint may be easiest as slope-intercept form: 5y<=2x+30, into {{{y<=(2/5)x+6}}}.


You would continue with this graph to pick your vertex points:

{{{graph(300,300,-7,7,-1,9,4,(2/5)x+6)}}}UNFORTUNATELY, entering x<=5 will not work in this rendering method, so it NEEDS to be included, but is missing.

Points to check will be (-5,4), (5,4), and  (5,8).