The relative humidity in the room at 16 degrees Celsius is 65%. How will it change when the air temperature drops by 4 K

The relative humidity in the room at 16 degrees Celsius is 65%. How will it change when the air temperature drops by 4 K, if the partial pressure of the water dad remains the same?

Answer: 84%.
Explanation:
phi = p / ph, p -parats. water pressure. couple.
to solve this problem, it is necessary to use the ratio:
phi2 / phi1 = phn1 / ph2, where phi2 and phi1 are the relative final and initial air humidity, respectively, phi1 and ph2 are the corresponding pressures of saturated water vapor in Pa. Find the pressure values at the corresponding temperatures from the lookup table:
pн1 (at t1 = 16) = 1.81 kPa; pH2 (at t2 = 16-4 = 12) = 1.4 kPa
We substitute:
phi2 = phi1 * pn1 / pn2 = 0.65 * 1.81 / 1.4 = 0.84 = 84%.