Elementary Theory – How do I refer to the only element in a singleton sentence?

You can rotate every element $ n $ into a singleton phrase by adding curly braces, $ {n } $, Is there an inverse to this operation, so if I know that the set is a singleton set, I can easily reference its element?

Suppose I have the set $ A = {5,6,7,8 } $and then a process that iteratively removes all elements except for one element of $ A $, and then I want to see what 10 plus is the resulting element, how could I write that?

The only way I can think of is to reference the first element by its index, e.g. $ 10 + A_1 $, Is there another way to do this? In my case the elements of $ A $ If there are already indices, I would have to index eg an index $ 10 + x_ {A_1} $, Which is not the worst thing in the world, I just wondered if there is a better way.