Answer:
In equilibrium, total output by the two firms will be option e= 300.   
Q =  +
 + 
Q = 100 + 200
Q = 300
Explanation:
Data Given:
Market Demand Curve = P = 1660-4Q 
where, P = price and Q = total industry output
Each firm's marginal cost = $60 per unit of output
So, we know that Q =   +
 +  
 
where  being the individual firm output.
 being the individual firm output.
Solution:
P = 1660-4Q
P = 1660- 4( +
 +  )
)
P = 1660 - 4 - 4
 - 4
Including the marginal cost of firm 1 and multiplying the whole equation by 
Let's suppose new equation is X
X =  1660 - 4
 - 4 - 4
 - 4
 - 60
 - 60
Taking the derivative w.r.t to  , we will get:
, we will get:
 = 1660 - 8
 = 1660 - 8 - 4
 - 4 - 60 = 0
 - 60 = 0
Making rearrangements into the equation:
8 +
 +  = 1660 - 60
 = 1660 - 60
8 +
 +  = 1600
 = 1600
Dividing the whole equation by 4
2 +
 + = 400
 = 400
Solving for 
2 = 400 -
 = 400 - 
 = 200 - 0.5
 = 200 - 0.5  
  
Including the marginal cost of firm 1 and multiplying the whole equation by 
P = 1660 - 4 - 4
 - 4
Let's suppose new equation is Y
Y =  1660 - 4
 - 4
 -4
 -4 - 60
 - 60
Pugging in the value of 
Y =  1660 - 4
 - 4 (200 - 0.5
(200 - 0.5  )  -4
)  -4 - 60
 - 60
Y =  1660 - 800
 - 800 +2
 +2 -4
  -4 - 60
 - 60
Y =  1600 - 800
 - 800 -2
 -2 
 
Taking the derivative w.r.t 
 = 1600 - 800 - 4
 = 1600 - 800 - 4 = 0
 = 0
Solving for 
4 = 800
 = 800
 = 200
 = 200
 = 200 - 0.5
 = 200 - 0.5  
 
Plugging in the value of  to get the value of
 to get the value of 
 = 200 - 0.5 (200)
 = 200 - 0.5 (200)
 = 200 - 100
 = 200 - 100
 = 100
 = 100
Q =  +
 + 
Q = 100 + 200
Q = 300
Hence, in equilibrium, total output by the two firms will be option 
e= 300.