kutulu

Look at the Clausius/Clapeyron equation:

DeltaH = - R* d(ln (Psat))/d(1/T)

it reduces to:

Ln(Psat2/Psat1) = -DeltaH/R*(1/T2 - 1/T1)

finally:

Psat2 = Psat1*exp(-DeltaH/R*(1/T2 - 1/T1))

DeltaH is the heat of evaporation (assume it's constant)
R is the ideal gas constant
T is absolute temperature
Psat is the vapor pressure

make Psat1 and T1 be the vapor pressure you know at the temp you know