Question 318406
{{{x+3<18}}}
{{{x<15}}}
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{{{2x+y<16}}}
{{{y<-2x+16}}}
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{{{x>0}}}
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{{{y>0}}}
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{{{drawing(300,300,-2,18,-2,18,grid(1),circle(8,0,.4),circle(0,16,0.4),circle(0,0,0.4),graph(300,300,-2,18,-2,18, -2x+16))}}}
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As you can see the constraint, {{{x+3<18}}} doesn't even enter into calculating the feasible region because the constraint, {{{2x+y<16}}} really identifies the region. 
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Check the value of the function at the three vertices:
(0,0):{{{f=50x+80y=50(0)+80(0)=0}}} 
(8,0):{{{f=50x+80y=50(8)+80(0)=400}}} 
(0,16):{{{f=50x+80y=50(0)+80(16)=1280}}}
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The maximum, 1280, occurs at (0,16).