Table:
text: 2007–08 Philadelphia Flyers season
Playoffs
Eastern Conference Semifinals
Date_ Visitor Score Home Decision Attendance Series
April 24 Philadelphia 3 – 4 Montreal Biron 21273 Canadiens lead 1–0
April 26 Philadelphia 4 – 2 Montreal Biron 21273 Series tied 1–1
April 28 Montreal 2 – 3 Philadelphia Biron 19849 Flyers lead 2–1
April 30 Montreal 2 – 4 Philadelphia Biron 19872 Flyers lead 3–1
May 3 Philadelphia 6 – 4 Montreal Biron 21273 Flyers win 4–1

Question: What was the average attendance on April 28 at the Eastern Conference semifinals, the 2007-08 season playoffs in Philadelphia?