One E1(PCM-30) has 32 time slots.
Of which 1 TS goes for Frame alignment and the other for signalling .
So totally v have 30 TS for traffic.
One TRX takes 2TS in the E1.Or in other words 1TS in the E1 takes 4 TCHs( i.e. 2TS for 1 TRX).
As we have left with 30 TS, 15 TRX can be accomadated or 15*8TCHs= 120 TCHs.