If a balloon at 25°C and a volume of 500 mL is cooled to liquid nitrogen temperature (77 K), what will be its volume (in mL)? Assume that this is a constant-pressure process.

Another Ideal Gas Law question - like your previous one, use PV=nRT. This time P, n and R are all constant, hence \frac V T is a constant. Can you take it from here? Be sure to ue temperature in degrees K.