I need to design a two's complement binary subtractor for an electronics test.

There needs to be two 3-bit inputs, one for the minuend and one for the subtrahend. The output needs to be the difference of the two numbers, eg. if the minuend and subtrahend are 2 and -1, respectively, the output should be 3. The design needs to include Boolean equations expressing each output bit in terms of the inputs.

The inputs should be represented as A2, A1, A0, and B2, B1, B0, with outputs of C2, C1, C0.

We have build an adder before on a different test, and I managed to do that, but for some reason, I can't seem to get my head around this one. I am getting confused about the "borrowing" part if the subtrahend is larger than the minuend, and I am not sure how to express negatives in the inputs. Any help will be greatly appreciated, and the sooner the better.

Thanks!