VS 2010 get the position of one string in other string ... but a little diffrent

suppose have a string like this :
"abcdsqr efgh(sqr)efg 655*sqr+876 resqrhhg sqrfdfd sqr uytu"
i want to get the position of "sql" in this string .this string is shown in red color in the top main string. but just the position of "sql" which left side and right character for it is :
1-space
or
2-numerical operator {"(", ")", "+", "-", "*", "/", "\", "=", "^"}
or
3-or both of them

by this condition my target strings in the top main string shown with green color:
"abcdsqr efgh(sqr)efg 655*sqr+876 resqrhhg sqrfdfd sqr uytu"
how can i get the start position of this?