A system of unknown configuration is fed by a step-function change of concentration. The following data are obtained for the exit concentration in elapsed time since the step change. Calculate the mean residence time using an integral approach:

t (min) or	C(t), mmol/cm
0	0
1.15	0.5
1.61	1.1
2.0125	2
2.3	2.85
3.45	4.2
4.6	4.7
5.75	4.9
6.9	4.95