[填空题]
A Carnot engine has a lower oeu jju+i 5ig68kre2hu y58e02k3a sxnperating t 7 9xcudv9vd-vemperature $T_L\,=\,20^{\circ}\,C$ and an efficiency of 30%. By how many kelvins should the high operating temperature $T_H$ be increased to achieve an efficiency of 40%? $K$
