Tend to Your Business

 is a quest in Fallout: New Vegas.

After replacing the Brotherhood elder with Head Paladin Hardin, he will ask you to go to Freeside and kill all the Van Graffs and their men to prove your loyalty.

Quick Walkthrough
The easiest way to complete this is to set C-4 Explosives down at the feet of each person in the Silver Rush. Since they aren't hostile to you, they will stay in place despite this. Then simply head to the bathroom, well outside the blast radius, and set the C-4 off with the Detonator.

You can kill them all during the botched arms deal to the Legion, then go back kill the doorman and you win.