XPATH expression to find node

[ghr2010]

I'm having troubles forming proper xpath expression to find data in xml similar to following:\[code\]<record><datafield tag="675" ind1=" " ind2=" "> <subfield code="a">791.221.4(71+44+469+450)(086.82)</subfield> <subfield code="c">791.2</subfield> <subfield code="s">791.2</subfield> <subfield code="b">791.2</subfield> <subfield code="v">UDCMRF 2006</subfield></datafield><datafield tag="702" ind1="1" ind2="1"> <subfield code="3">39609187</subfield> <subfield code="a">Cronenberg</subfield> <subfield code="b">David</subfield> <subfield code="f">1943-</subfield> <subfield code="4">300</subfield> <subfield code="4">690</subfield></datafield><datafield tag="702" ind1="0" ind2="1"> <subfield code="3">16448611</subfield> <subfield code="a">Suschitzky</subfield> <subfield code="b">Peter</subfield> <subfield code="4">600</subfield></datafield><datafield tag="702" ind1="0" ind2="1"> <subfield code="3">8497763</subfield> <subfield code="a">Shore</subfield> <subfield code="b">Howard</subfield> <subfield code="4">230</subfield></datafield></record>\[/code\]How to build an expression that basically says: search datafields with tag value 702 and return me surname and name of person that has value 300 in subfield with code 4 - so that the answer in this case would be Cronenberg David?Thanks in advance.