Ramanand Desai, the local shopkeeper mixed three qualities of pulses P1, P2 and P3 priced at Rs 74 per kg, Rs 68 per kg and Rs 63 per kg in the ratio of 1:2:4. He added some more quantity of P1 to 4 kg of this mixture. He sold this new mixture of Rs 84 per kg, thereby making a profit of 20%. How much of P1 did he mix with the mixture?