given it is 16 bit instruction format means no of en codings will be 2^16
5 bits are reserved for address field
so en codings for 2 2 address instructions will be 2^5*2^5*2=2048
en codings for 1024 1 address instructions will be 2^5*1024=2^15=32768
then en codings for 0 address instructions will be=(total en codings-(en codings for 2 address+en codings for 1 address)
ans=2^16-(2048+32768)
=65536-34816=30720