Pressure by whistle = Po + F / A = Po + mg/ A
= 105Pa + (0.1 * 10 N) / (0.1 * 104 m2)
= 2 * 105 Pa
Pressure inside cooker = 105Pa
for whistle to just lift, by gay lussacs law
Pwhistle / Tsurrounding = Pcooker / Tcooker
(2 * 105 Pa) / 300 K = 105 Pa / T
T = 600 K = 327oC