A first-order homogeneous reaction of A going to 3B is carried out in a constant pressure batch reactor. It is found that starting with pure A the volume after 12 min is increased by 70% at a pressure of 1.8 atm. If the same reaction is to be carried out in a constant volume reactor and the initial pressure is 1.8 atm, calculate the time required to bring the pressure to 2.5 atm.