A Carnot engine whose low temperature reservoir is at $35$C has an efficiency of $0\mathrm{.}4.$ Your boss wants to increase the efficiency to $0\mathrm{.}65.$ By how many degrees the temperature of the hot reservoir be increased? Write the temperature in the unit of Kelvin. $($The temperature of the cold reservoir is kept unchanged.$)$ A Carnot engine whose low temperature reservoir is at $\backslash (35^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ has an efficiency of $0\mathrm{.}4.$ Your boss wants to increase the efficiency to $0\mathrm{.}65.$ By how many degrees the temperature of the hot reservoir be increased? Write the temperature in the unit of Kelvin. $($The temperature of the cold reservoir is kept unchanged.$)$