Suppose you are playing game of shooting balloon. You expect to shoot $n$ balloons in the board, assuming you are sharpshooter, $100\%$ hit. There are two scenarios, you need find the appropriate Big$-$Oh notation for the following question. Note that one unit of work is shooting one balloon.

"For every $2$ balloons you can shoot, one new balloon is inserted in the board. So$,$ if there were $20$ balloons, after you shoot the first $2,$ there are $19$ on the board. After you shoot the next $2,$ there are $18$ on the board. How many balloons do you shoot before the board is empty?"

Note: Find your answer as a function of $n.$ Don't just justify on the number $20$ since it is just an example.