Question 71877
{{{15x + 20y <= 300}}}
divide by 5
{{{3x + 4y <= 60}}}
{{{x >= 4}}}
{{{y >= 3}}}
{{{x + y <= 18}}}
I can determine that
{{{x + y >= 7}}} from above 
I now have 3 inequalities I can plot
{{{ graph( 400, 400, -5, 30, -5, 30, (-3x + 60)/4, -x + 18,-x + 7) }}}
The feasible area is the smallest area bounded by
the 3 lines. You can pick values that are just inside
or just outside to test them by putting into the inequalities