Total number of possible instruction encoding = 2^16
This CPU has three type of instructions
Number of possible instruction encoding for Type I (2 address instruction)= 12 * 2^6 * 2^6
Number of possible instruction encoding for Type II (1 address instruction)= 12 * 2^10
Let number of possible instruction encoding for Type III (0 address instruction) be x
Since , Type I+ type II+ Type III= 2^16
=> 12 * 2^6 * 2^6 + 12 * 2^10 + x = 2^16
=> x = 4096
Number of zero address instruction possible = 4096