I'm on the chapter/level 7 and I'm in the gladiator pit in the 'strip club'. I have to preform 3 executions but it won't let me. How do I do this?

I'm on the chapter/level 7 and I'm in the gladiator pit in the 'strip club'. I have to preform 3 executions but it won't let me. How do I do this?