For the reaction, P + Q + R → S, experimental data for the measured initial rates is given below:

Expt.	Initial conc. P (M)	Initial conc. Q (M)	Initial conc. R (M)	Initial rate (m/s)
1	0.2	0.5	0.4	8.0 × 10-5
2	0.4	0.5	0.4	3.2 × 10-4
3	0.4	2.0	0.4	1.28 × 10-3
4	0.1	0.25	1.6	4.0 × 10-5

The order of the reaction with respect to P, Q and R respectively, is