If you look up "angles of 7 sided polygon" it would give a result of how many degrees polygons with 7 sides such as this one above would equal to. It's important to know that when finding x angles within.
7-sided polygons = 900 degrees in total
Since all the other angles except x are given, we can add all those up and set it equal to 900. So it would look like this:
Simply solve for x now.
So x = 111 degrees.
Hope this helps!