OK, maybe I'm a lil' late but this can be saved for future ref. so, heres a link for learning about Functions:
http://www.mathsisfun.com/sets/function.html-it helped me when I forgot how to do it
and you also need to know about inverse functions:
http://www.mathsisfun.com/sets/function-inverse.html-It's easier to find out the inverse if you use algebra, like this(also already shown in the link I gave) :
The function: f(x) = 2x+3
Put "y" for "f(x)": y = 2x+3
Subtract 3 from both sides: y-3= 2x
Divide both sides by 2: (y-3)/2 = x
Swap sides: x = (y-3)/2
Solution (put "f-1(y)" for "x" and replace y in "(y-3)/2" with "x") : f-1(y) = (x-3)/2
-they're used whenever u see a format like this: f(x)=bla+bla (in questions the 'f' can be replaced with any letter, 'x' can sumtimes be given as a number, and it doesnt have to be addition. depends on their question)
Hope this helps
