A number divided by 3 is - 11. What is the number?

Call the number x for now. It is a placeholder for the answer.

"A number divided by 3" translates to x/3 where the slash means division.

"A number divided by 3 is - 11" means we have this equation:

x/3 = - 11

To solve for x, we multiply both sides by 3. Why multiply? Because we want to undo the division operation done to x. This will get x all by itself.

Doing so leads to ...

x/3 = - 11

3 * (x/3) = 3 * (-11)

x = - 33

So the unknown number is - 33

As a check

x/3 = - 11

-33/3 = - 11

-11 = - 11

so the answer is confirmed

The answer would be - 33