Question

16-9 add them in binary using 2's complement to represent the negative number

Answer 1

In two's-complement representation, positive numbers are simply represented as themselves, and negative numbers are represented by the two's complement of their absolute value

Note that to get the two's complement of -9 start with
01001, which is just 9 in regular binary

Then, since this is negative, invert all bits and add one
10110
+ 00001
________
10111

This is the two's complement of -9.

Now just use regular binary arithmetic with carries.

10000 (16)
10111 (-9)
___________
00111 (7)