What number goes in the “?”

? - 2x - 5 = 5

First, replace the “?” with an x:
x - 2x - 5 = 5

Next, combine alike terms:
[ x - 2x ] - 5 = 5
^ alike terms

This will result in:
-x - 5 = 5

You do the inverse (opposite) of -5
-x -5 = 5
+5

Once you do the plus 5, the five moves to the end of the equation:
-x - 5 = 5 + 5
+5>>>>>^

The “-5” no longer exists because you canceled it with the “+5” that you moved to the other side.
The new equation:
-x = [5 + 5]
^ you add these two

After adding you get:
-x = 10

When putting “x” into a number it will ALWAYS be 1.

You then divide both sides by the “x” (which is -1 since it it always equal to one but is negative because it has a negative sign on it)

Your new equation:
-x / -1 = 10 / -1

If you divide to negatives, this will result in a positive.

You’re left with:
-x / -1 = x (since two negatives become a positive result)
10 / -1 = 10 (if there’s a negative and positive when dividing, it will automatically become negative) [ONLY FOR DIVISION]

At the end you’re left with:
x = -10

hope this helps