Proving in computability if L is subset of RE and infinity there is A ⊆ L and decidable

Question

I'm trying to prove this in Computability: if $L$ is a subset of Recursively Enumerable \ Recursively ($RE \setminus R$) and $L$ is infinite, so there is $A \subseteq L$, which is infinite and decidable. I don't even have any idea where to start, I understand I need to minimize $L$ to a decidable set.