Answer:
-$55
Explanation:
The computation of the marginal revenue is shown below:
As we know that
Total revenue = Price × Quantity
For 400 units, the total revenue is
= 400 × $50
= $20,000
And for 420, the total revenue is
= 420 × $45
= $18,900
Now the marginal revenue is
= ($18,900 - $20,000) ÷ (420 units - 400 units)
= -$55