$\backslash$table$[[\backslash$table$[[$Number of$],[$Security Lines$]],$Marginal benefit $($$$),$Marginal cost $($$$)],[1,15,000,3,000],[2,13,500,4,500],[3,10,500,6,000],[4,7,500,7,500],[5,6,000,12,000],[6,4,500,18,000]]$

The surplus of benefit over cost for the second security line is equal to $ $$

The surplus of benefit over cost for the third security line is equal to $ $$

Suppose your goal is to maximize the total surplus. You $$ want to operate the third security line.

The optimal number of TSA security lines is $$