Answer:
Answer : Economic Cost = $80.000
Normal Rate of return = 300 % 
Economic Profit = $40, 000 
Accounting Profit = $90,000 
 
Step-by-step explanation
Total Revenue = $1,20000 
 
Total Cost = $30,000 +$50,000 
 
Oppotunity cost is included in Economic Cost. 
 
Hence EC (Economic Cost) = 30,000+50,000 
 
= $80,000 
 
Normal Rate of return = (1,20000 - 30,000)/ 30,000 
= 300 % 
 
Accounting Profit = Total Revenue - Explicit cost 
 
= $120,000 -$30,000 
 
= $90,000 
 
Economic Profit = $120,000 -$30,000 - $50,000 
 
= $40, 000 
 
Relationship between Average Total Cost (ATC) and Marginal Cost (MC)
 
When MC falls, ATC also falls but rate of fall is higher in ATC. 
ATC cuts MC where ATC is minimum.