To solve this, we just need to break down the problem. We can form our equation by doing so.
"The difference"
This tells us that we are doing a subtraction problem.
-
"of a number"
This shows that it will be a variable minus something.
n-
"and 7"
This shows that our next number will be 7.
n-7
Using the logic above, we can see that the equation to represent this is n-7.