Question 163200
I think you have an incorrect equation because non of your optional answers mahch the equation.
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C(x) = 900 / (x + 30)
c(x)=900/630
c(x)=1.428 is the cost per unit.

c(600)=900/600+30
c(600)=1.5+30
c(600)=$31.50 is the cost per unit of plywood.