To solve this question, we can start to set up an equation using what the question is telling us. Since we don't know what the number is, let's make it equal to x.
The phrase "5 times a number" means that we're multiplying our unknown, x, by 5. That is equal to 5x. 9 less than that would be 5x - 9. Since we know that it's equal to -30, we can solve.
5x - 9 = -30
Get all terms with x on one side and the constants on the other
5x - 9 +9 = -30 + 9
Simplify
5x = -21
Now, we can divide both sides by 5 to get our answer of x = -