How many $[$kg$]$ of groundwater at $10[]$ are needed to cool $1[$kg$](539$ kcal$/$kg$)$ of water vapor at $100[]$ to $39[$C$]$ in a double pipe heat exchanger? $($However$,$ the discharge temperature of the coolant is $70$ and the body arrangement is $1.)$

In a double pipe heat exchanger, $1[$kg$]$ of water vapor at $100[]$ is cooled to $(2539$ kcal$/$kg$)50[$C$].$ If $9\mathrm{.}8[$kg$]$ of groundwater at $10[]$ is required, the discharge temperature of the cooling water is $[$ t$]?$

$($However$,$ the specific heat of water is $1.)$

In the double heat exchanger, the inlet temperature of the external high$-$temperature fluid was $110[]$ and the outlet temperature was $100[],$ and the inlet temperature and outlet temperature of the low$-$temperature fluid of the inner plate were $20[]$ and $75[].$ If it flows countercurrently, what is the logarithmic average temperature difference $[$C$]?$