Question 353053
{{{graph(300,300,-5,20,-5,20,(72-4x)/3,(174-6x)/10)}}}
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{{{a}}},{{{b}}},and {{{c}}} are all valid vertex points. 
{{{d}}} is not. 
Check the value of z(x,y) at all 3 locations to find the minimum value.
({{{18}}},{{{0}}}):{{{z=5x+15y=5(18)+0=90}}}
({{{0}}},{{{17.4}}}):{{{z=5x+15y=5(0)+15(17.4)=261}}}
({{{9}}},{{{12}}}):{{{z=5x+15y=5(9)+15(12)=225}}}