from 9 to 9h15: 0.2 erlang means ckt/s occupied for 3 minutes in 15 minutes observation (Erlang is occupancy of circuit divided by observation period)
from 9h15 to 9h30: 0.3 erlang means ckt/s busy for 5 minutes in 15 minutes
from 9h30 to 9h45: 0.1 erlang means ckt/s busy for 1.5 min(90 sec)in 15 minutes
from 9h45 to 10: 0.4 erlang means ckt/s busy for 6 minutes in 15 minutes.
In one Hour duration occupancy comes to (3+5+1.5+6)min=15.5 min
ie 15.5/60 around 0.25E in 1Hour