f(x) = 3x + 1
f(9) = 3(9) + 1
f(9) = 27 + 1
f(9) = 28
f(9) = 28. I hope this helps! I have a g00gle classroom where I help with algebra including this. If you are interested, please consider joining. I will post the class code in the comments if it would let me. Sorry it wouln't let me type g0ogle properly.