A425-ml sample of hydrogen is collected above water at 35°c and 763 torr. find the volume of the hydrogen sample when the temperature falls to 23°c, assuming the barometric pressure does not change. (vapor pressures of water : at 35°c, 42.2 torr ; at 23°c, 21.1 torr)

From the gas laws, Charles law states that the volume of a fixed mas of a gas is directly proportional to absolute temperature at constant pressure.
and Boyle's law states that the volume of a fixed mass of a gas is inversely proportional to pressure at constant temperature, therefore combining the two we have, PV/T, for two gases we have,
P1V1/T1=P2V2/T2
V1 = 425 ml, T1= 35 +273 =308 K, P1= 805.2 torr
V2 = ?  and T2 = 23 +273 = 296K, P2 = 784.1torr
  V2 = P1V1T2/P2T1
       = (805.2×425×296)/784×308
       = 419.486 ml
       = 419.5 ml