Answer: c). decreases by $1.80
Step-by-step explanation: Economic surplus is the sum of consumer surplus and producer surplus. When the marginal benefit is less than marginal cost, producing one more unit will lower the economic surplus by and amount equal to the difference between marginal benefit and marginal cost.
![image](https://img.qammunity.org/2019/formulas/business/college/6fqnl1mu4ya3mayd18zda8v023co4qjstu.png)
Therefore, economic surplus decreases by $1.80, which is option c.