Answer:
0.99c + 9.99
Explanation:
We know one part of the expression is going to be $0.99c, since it's $0.99 per custom skin, and c is the number of custom skins were getting.
Then we must add on the 9.99 on top of that, since that is the one-time membership fee. This is what the equation looks like :
0.99c + 9.99
Hope this helps :)