###### Example2.3.3

If a number plus $$2$$ is $$6\text{,}$$ what is the number?

One way to solve this riddle is to use the opposite operation. If a number plus $$2$$ is $$6\text{,}$$ we should be able to subtract $$2$$ from $$6$$ and get that unknown number. So the unknown number is $$6-2=4\text{.}$$

in-context