Perform the 2's complement subtraction of smaller number (101011) from larger number (111001).

To subtract a smaller number from a larger one with 2's complement, we add the 2's complement of the smaller number to the larger number. The final carry out is thrown away.

The 2's complement of $101011$ is found by inverting every bit, which gives $010100$, and then adding 1:

$$010100 + 1 = 010101$$

Now add this to the larger number:

$$111001 + 010101 = 1,001110$$

The extra carry bit $1$ on the left is discarded. Therefore the answer is $001110$, which is $14$. Check: $57 - 43 = 14$.