Sure, let me help you on this one!
In order for us to find a percentage, we need to transform the amount of percent we want to find into decimal form.
80% = 0.8
Then, our job is to multiply that decimal form number by a number we are interested finding percentage in.
In our case, this number is the amount of 6th grades - 685 students.

Answer: 548 students at the Harrison Middle are going on a field trip to the Museum.