Traffic offered = traffic carried + traffic blocked.
With the number of links and the traffic carried you can evaluate the traffic offered with the inverse formula of Erlang B. But if the system retries the blocked calls then you need the inverse extended formula.
You can only evaluate traffic offered with inverse Erlang B if the blocking is exclusively radio resource blocking ie you assume there is no blocking due to call processing failures.
The most accurate way,in my opinion,is to calculate offered traffic= carried traffic/1-Blocking(0.0001 to 0.9999)