Answer: A) 9
Explanation:
First of all, we need to compute the traffic intensity in Erl.
If we take the busy hour, for 60 calls of 60 sec each, we would have 100% occupied the circuit, which we define as 1 Erl.
Making a simple comparison, if we have half of calls, with half duration each, we will have the circuit busy 25% of time, i.e. 0.25 Erl.
The CCS is a unit of telephony traffic, that measures it in units of 100 call-seconds (calls that last 100 seconds), and is equivalent to 1/36 Erl, due to we can show that 1 Erl = 36 CCS
(If we had 36 calls of 100 sec each (100 CCS), we would have the circuit busy 100% time, i.e., with 1 Erl traffic).
If we know then that 1 Erl= 36 CCS, we can find out how many CCSs are equivalent to 0.25 Erl, solving a simple direct proportion, as follows:
36 CCS/ 1 Erl = x CCS/ 0.25 Erl ⇒ 9 CCS
