The sum of two numbers is 30 and their difference is 6

I'm going to assume that you are trying to find the two numbers. Based on the information in the problem, we can create the following equations (where and are the two numbers):

We have a systems of equations. In this case, it would be easier to use elimination by adding vertically. This produces the result:

To find , substitute the value for into one of the earlier equations:

The two numbers are 12 and 18.