"if i didn't have class tonight, i would save the $4 campus parking fee and spend four hours at work where i earn $10 per hour." the opportunity cost of attending class this evening is:

Opportunity Cost = It is the cost that is to be sacrificed for achieving something else.  
Given: - 
Campus parking fess (class) = $4 
Income earned through working for 4 hours in place of attending class = $40 ($10/hr) 
 Solution: -  
Opportunity cost of attending class = $4 + $40 = $44.

Gogogoggo go go somewhere