Describe the rule shown in the image. If the input is x, what is the output?

The first box indicates that you need to add 12 to the input.
If the input is $x$, the result after the first step is $x + 12$.

The second box indicates that you need to subtract 6 from the result of the first operation.
Taking the result from Step 1, which is $(x + 12)$, you then subtract 6.
So, the output is $(x + 12) - 6$.

Combine the operations:

The overall rule is to add 6 to the input.

Therefore, for any given input, you first add 12, and then subtract 6 from that result. This is equivalent to simply adding 6 to the original input.