String Comparison

Hi,

Let's say we have two strings, as follows:

STRING_A    VARCHAR2(100) := '60';

STRING_B    VARCHAR2(100) := '006,6,060,600,60,666,0060';

I would like to compare STRING_A to STRING_B to find only the value '60'.   

Can you recommend a way to do this?

Thank you for your help.

p.s.  We use Oracle 11G.