1. ## I need helppppppppp

, , and
what is the Pf

2. ## Re: I need helppppppppp

19 = 9*[1/(1-Pf/478)]
=> 19/9 = 1/((478 - Pf)/478)
=>19/9 = 478/(478-Pf)
=>19(478-Pf)=478*9

I think you can take it from here