Okay, I'm going to stretch this explanation long so people can understand! Hopefully this helps :) I will also provide a shorter explanation so if people want to find out how to do it quicker without details to help you understand better, they can read the shorter explanation!

- long explanation -

Equation provided from the info :: (x * 2) + 1 = 15

We need to find out what number is the x. First of all, one way to do it is do the equation backwards. And the operators will be the opposite too, for example addition is the opposite of subtraction and multiplication is the opposite of division. Now once we flip the equation it should look like this:

(15 - 1) / 2 = x

Let's break the equation apart so it's easier to work with. Remember, the rule PEMDAS. Parentheses, Exponents, Multiplication and Division, Addition and Subtraction. Why I put "and" between some words, is because they are the same level and you should go left to right from the equation. So the equation in parentheses is (15 - 1). So we just have to solve it! The answer is 14, which is an even number, so we don't have to fiddle with decimals. But if you want to know how to divide an odd natural number, feel free to comment on this answer! The equation should look like this:

14 / 2 = x

Now, all we have to do now is divide 14 in half! As someone who memorised their whole multiplication and division table, it's easy for me to figure it out. But if you haven't, try using addition! All you have to do is count up your numbers.

1 + 1 = 2

2 + 2 = 4

3 + 3 = 6

4 + 4 = 8

5 + 5 = 10

6 + 6 = 12

7 + 7 = 14!

So now we know 14 / 2 is 7. Sorry if this is too easy, I'm just giving attention to some who learn slowly, which is absolutely alright! So now we have our 2 answers. The equation now looks like this:

14 / 2 = 7.

Well we now know what the x is, and if you want to make sure it's the correct answer just flip the equation!

(7 * 2) - 1

7 * 2 = 14

14 - 1 = 15

Your answer is the same one provided, so the number is 7!

- short explanation -

The equation with the numbers provided is (x * 2) + 1 = 15

Let's flip the equation so it's easier! It should look like this:

(15 - 1) / 2 = x

Now all we have to do is solve it!

15 - 1 = 14