Asyringe containing 1.45 ml of oxygen gas is cooled from 90.4 ∘c to 0.5 ∘c. what is the final volume vf of oxygen gas? (assume that the pressure is constant.)

Charles law gives the relationship between volume and temperature.
It states that at constant pressure, volume of gas is directly proportional to temperature of gas. 
V/T = k
where k - constant 

where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation 
temperature should be given in K
T1 - 90.4 °C  + 273 = 363.4 K
T2 - 0.5 °C + 273 = 273.5 K 
Substituting values in the equation 

V = 1.09 mL
Final volume is 1.09 mL