Answer:
f(k) = 2*k + 1
Explanation:
The 'f' function takes the variable, doubles it, and then adds 1.
So f(k) = 2*k + 1
f(g) = 2*g + 1
f(m) = 2*m + 1, and so on
It doesn't really matter which variable you use, the function still does the same thing to it.