f (n) {(n)/(2) 3n +1 if n is even

if n is odd

This is an example of why some questions go unanswered.

You post some kind of problem, about which many possible questions could be asked.
You give no indication of what it is you want to know.
We don't mind helping to find the solutions, but don't make us come up with the questions as well!

well then what we need to find out is what is 0/3 which is basically impossible.

since 0 cannot be divided.

Clearly you arent smart enough to realize that is the question.

Dont say anything if you dont understand it.

Simplifying

f(n) = 2f(n + -1) + 3n

Multiply f * n
fn = 2f(n + -1) + 3n

Reorder the terms:
fn = 2f(-1 + n) + 3n
fn = (-1 * 2f + n * 2f) + 3n
fn = (-2f + 2fn) + 3n

Solving
fn = -2f + 2fn + 3n

Solving for variable 'f'.

Move all terms containing f to the left, all other terms to the right.

Add '2f' to each side of the equation.
2f + fn = -2f + 2fn + 2f + 3n

Reorder the terms:
2f + fn = -2f + 2f + 2fn + 3n

Combine like terms: -2f + 2f = 0
2f + fn = 0 + 2fn + 3n
2f + fn = 2fn + 3n

Add '-2fn' to each side of the equation.
2f + fn + -2fn = 2fn + -2fn + 3n

Combine like terms: fn + -2fn = -1fn
2f + -1fn = 2fn + -2fn + 3n

Combine like terms: 2fn + -2fn = 0
2f + -1fn = 0 + 3n
2f + -1fn = 3n

Combine like terms: 3n + -3n = 0
2f + -1fn + -3n = 0

The solution to this equation could not be determined.
noice.

Meaning the answer is a repeated 0

@oobleck The question was there you didn't take enough time to think about the question, also in the real world you wont have instructions you will just have to figure out what to do. This is an example of why kids should spend more time studying or doing something productive rather than nolifing a game 18 hours a day.