I am a recent Civil PE in Connecticut and I had a Chemical Engineer and a Mechanical Engineer as two of my five references. It all depends on the state, but I know Connecticut standards are usually similar to MA and other New England States. It should be pretty clear on the State's website...
You don't have time to work out more complex algebra by hand during the exam. Use the SOLVE function on your calculator. Literally just enter the equations exactly as you have written and hit the solve button. It is very easy on a Casio fx-115ES. There are youtube videos that can walk you...
I just got mine this weekend. I have to say that I am very disappointed in the design compared to most other states wall certificates I have seen. I almost don't want to frame and display it because it looks so cheap. Not even a state seal on it.