The relation between the volume, pressure and temperature of gases is shown using the following equation:
(pressure x volume)1 / temperature1 = (pressure x volume)2 / temperature2
This relation is actually established by combining the three gas laws (Boyle's, Charles's and Gay-Lussac's)
At constant pressure,
(volume/temperature)1 = (volume/temperature)2
128/20 = v2/40
Volume = 256 ml
