Question 79335
C=mx + b
b=fixed cost=40
m= variable cost=10
Plug-in the values:
C=10x+40
This means that the fixed cost will always be $40.00 regardless of the number of items (x).  The fixed cost is the overhead or the standing cost of doing business.  It won't change.  
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The varied cost will be $10 times the number of items.  So if you have 2 items, multiply it by $10 ($10 x 2=$20), plus the fixed-cost of $40.00 = $20+$40=$60

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Or if x=2, than
C=10x+40
C=10(2)+40
C=20+40
C=$60