The difference between eight times a number and seven more than seven times that number

First, 8 times a number can be represented by 8x
Then, seven more than seven times that number can be represented by 7x+7

So if we need the difference between these two terms, it would be:
8x-(7x+7) (distribute the negative)
8x-7x-7 (combine like terms)
x-7

Hope this helps