Remove parentheses with regexp

I have the following string:

 a ='0.00 (578)';

How can I use regexp to retrieve what is inside the parentheses?

I have used this

 regexp('0.00 (578)', '\S*\s', 'match')

but it gives me:

 '0.00 '

Answer 1

[Azzi Abdelmalek]

a ='0.00 (578)';
regexp(a,'(?<=\()[\d.]+(?=\))','match')

[Giorgos Papakonstantinou]

Thank you Azzi!