Erlang B Calculation for ISDN BRI Ports

I work for a company dealing with products and solutions for telecom operators’ wireline access networks.
We are trying to figure out how to consider the operator’s Erlang
requirements for ISDN BRI subscribers and which numbers we should put in the Erlang B calculator. We have 3 options in mind:
1. Multiply the number of ISDN BRI ports by the required Erlang per subscriber, and enter this number into the BHT parameter in the calculator. The result (lines) would be the number of equivalent ISDN BRI ports that should be allocated, and this number should be multiplied by 2.25 (2B + D) to get the number of timeslots that are required.
2. As above, but the result (lines) should be considered as the number of required timeslots (multiplication by 2.25 is not required).
3. Multiply the number of ISDN BRI ports by 2.25 (2B + D) to get the equivalent number of timeslots, then multiply this number by the required Erlang per subscriber, and enter this number into the BHT parameter in the calculator. The result(lines) would be the number of timeslots that are required.

Can you please answer which of the above options is correct, or if
none of them is correct, what is the correct one?
Please note that each option gives different results. If you want a real example, take 48 ISDN ports, 0.3 Erlang per subscriber and 0.01 blocking.

Thanks,
Eduard