Your number incremented by 1 is 8
Your number, incremented again by 1, is now 9. If we store that operation, its value is also 9.
Let's start over, with your original number 7
Again, your number incremented by 1 is 8
Now we store the value of your number in a second variable, which is now equal to 8, and then we increment your number again. It's now 9.