Table:
text: V/Line G class
Fleet list
Fleet list
Locomotive Serial_No Entered_service Owner_ Operator_ Livery Gauge Status_
G538 89/1271 May 1989 Pacific National Pacific National Freight Australia green & yellow Standard Operational
G539 89/1272 June 1989 Pacific National Pacific National Pacific National blue & yellow Broad Operational
G540 89/1273 August 1989 Pacific National Pacific National Freight Australia green & yellow Standard Operational
G541 89/1274 September 1989 Pacific National Pacific National Freight Australia green & yellow Standard Operational
G542 89/1275 October 1989 Pacific National Pacific National Freight Australia green & yellow Broad Operational
G543 89/1276 November 1989 Pacific National Pacific National Freight Australia green & yellow Standard Operational

Question: What is the serial number of the Class V/Line G locomotive that entered service in October 1989?