I have a couple of questions to ask on some algebra. I have an upcomming exam and i just wanted to see if you guys could help me out and explain how these are done. thank you very much.

1) Given f(x)= 3-x^2 find f(t-1)

i could not figure this out correctley, i kept on comming up with t^2-2t+1 but my proffesor says this is incorrect.

2) Given f(x)=1/(x+1) and g(x)=(x+1)/3x, what is (g o f)(x)?

ive had a lot of difficulty with these types of problems and can never figure them out.

3) Solve (4/5)n + 2= -3(3/4n -8)

I think my brain is going out because i have tried this problem at least 10 times and can't seem to get it right.