The Raiders traveled across the bay to Monster Park in San Francisco to take on the 49ers. The 49ers got on the board first with an Alex Smith to Arnaz Battle touchdown pass midway through the first quarter.  The Raiders responded with a 33-yard field goal by Sebastian Janikowski.  Janikowski then converted a 36 yarder early in the second quarter.  Randy Moss scored his 100th career touchdown reception on a 22-yard pass from Andrew Walter, as the Raiders went into halftime with a 13-7 lead. The 49ers then went on to score 24 unanswered points in the second half, as Smith connected on touchdown passes with Battle once again, and Maurice Hicks in the third quarter.  Joe Nedney converted a chip shot 19-yard field goal early in the fourth quarter. On the next Raiders play from scrimmage, Melvin Oliver recovered a fumble for a touchdown, as Walter tried to lateral a pass to LaMont Jordan, who let it hit the ground, and assumed it was an incomplete pass.  Marques Tuiasosopo hit Courtney Anderson with a touchdown pass late in the game, but it was too little too late.  Nedney completed the scoring with a 39-yard field goal.
Question: How many points did Oakland lead by at halftime?
Answer: 4