Odd or even?

Maths

Is the value of 2n always odd, always even, or either?

Is the value of 4n - 2 always odd, always even, or either?

Is the value of 3n + 1 always odd, always even, or either?

What operation could I perform to 4n + 1 to make it always even?

What operation could I perform to n + 4 to make it always even?

What is the final answer if I start with 4?

What is the final answer if I start with 6?

Will the answers to the puzzle above always be odd, even, or does it depend on the starting number?