We're going to go ahead and create a few grades. First up, let's create a grade with an id of 1. Now, this 1 is going to be attached to Andrew, so we'll go ahead and use the schoolId to do that. The schoolId, in this case for Andrew, is 101. Then, we're going to put in the actual grade. In this case, I'll go ahead and give myself an 86:

const grades = [{
  id: 1,
  schoolId: 101,
  grade: 86
}];

This is grade 1; let's go ahead and create three more grades. I'm going to copy it, toss in a comma, and paste it two times. This one is going to have an id of 2. We can associate this one with Jessica, so we'll give her the schoolId value of 999. She's really smart so we'll give her a 100. Finally, id of 3: we'll leave this one associated with Andrew and, next, we'll give him a grade of an 80:

const grades = [{
  id: 1,
  schoolId: 101,
  grade: 86
}, {
  id: 2,
  schoolId: 999,
  grade: 100
}, {
  id: 3,
  schoolId: 101,
  grade: 80
}];

So, we have some grades in place and the goal is to return all of the grades for a particular student based off of their schoolId. If I pass in 101, I would expect an array to come back with the object associated with Andrew. If I pass in 999, I would expect an array to come back with the one associated with Jessica, and if I pass in a value like 55, there are going to be no grades for that student, so we'll go ahead and return an empty array.