Answer:
The equilibrium quantity of widgets has fallen by 40 per month (Option A).
Explanation:
Equilibrium quantity was 200 units when there was no tax.
When a $5 tax per unit was imposed, the government revenue is calculated as (200 *$5) = $1000
But the government revenue provided in the question is $800, which means the loss in government revenue is ($1000 - $800) = $200.
Thus, the quantity loss is ($200 / $5) = 40.
In conclusion, the equilibrium quantity of widgets has fallen by 40 per month.