Question 64672
The maximum value of z = 20x + 8y subject to 

3x + y <= 8
2x + 5y <= 18
x => 0, y <=0 is

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Graph:
y<=-3x+8
Graph:
y<=(-2/5)x+(18/5)
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Find the intersection point of the equations and their x and y intercepts
-3x+8=(-2/3)x+18/5
(-7/3)x=18/5-40/5
(-7/3)x=(-22/5)
x=66/35=1.8857
y=(-3)(-66/35)=198/35=5.657
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{{{graph(300,200,-10,10,-10,10,-3x+8,(-2/5)x+(18/5))}}}
The important points are (0,0),(0.18/5),(8/3,0),(66/35,198,35)
Substitute those values into the "z" formula and see which gives
you the greatest value for z. 
Cheers,
Stan H.