设铁的比热是a J/(K·g),末温为t°C:
1.5*a*(800-t) = 538.2
t = 800 - 538.2/(1.5a)
= 800 -358.8/a
查得铁的比热是：铁的比热为0.46J/(K·g)
t = 800-358.8/0.46
= 800 - 780
= 20 °C