Subtract using 1’s complement: 9-12

Step 1: Convert the numbers into binary

• 9 in binary is 1001
• 12 in binary is 1100

Step 2: Find 1's complement of the second number (12)

• 1's complement of 1100 is 0011

Step 3: Add the first number and 1's complement of the second number

• 1001 (9 in binary)

• 0011 (1's complement of 12) = 1100

Step 4: If there is a carry, add it back to the result

• In this case, there is no carry, so we skip this step

Step 5: Take the 1's complement of the result to get the final answer

• 1's complement of 1100 is 0011, which is 3 in decimal

So, 9 - 12 = -3 in decimal.