how to insert the narrowband 48 subacarrier(3.75kHz) grid to the LTE12 subcarrier(15kHz) empty grid

NB-IoT resource block (180kHz) is deployed in LTE inband and guardband. NB-IoT 48 subcarriers each 3.75kHz and LTE resource block is 12 subcarriers each 15kHz. have to insert the NB-IoT PRB block to the allocated PRB indexes in the LTE carrier. When mathematically considered the case, the matric sizes are different becasue there 48 rows in NB-IoT matric and 12 rows in LTE matric. So how to do that one