15% of the students in Mr. Riley's social studies classes watch the local news every night. Mr. Riley found that 136 of the students do not watch the local news. How many students are in Mr. Riley's social studies classes?

What we are saying here is 136 students represent the rest of the students which is 100% minus 15% or 136 represents 85%. All we need to do (there are several ways but I prefer this one) divide 136 by 85 then multiply by 100 to find answer which is 160