From ideal gas equation, pV=(n1+n2+n3)RT where, n1= number of moles of oxygen =3216n2= number of moles of nitrogen =2828n3= number of moles of carbon dioxide =4444
⇒pV=[3216+2828+4444]RT=[21+1+1]RT
=25RT⇒p=25VRT This is the required pressure of the mixture of the gases.