college chemistry
posted by Haley .
A sample of helium occupies 1521 mL at 719 mmHg. Assume that the temperature is held constant and determine
a) the volume of the helium at mmHg.
b)the pressure, in mmHg, if the volume is changed to 315mL

You omitted the number for a but what you want is P1V1 = P2V2. Substitute and solve for the unknown v.
b. Use P1V1 = P2V2 again. Substitute and solve for the unknown.