Problem in GradeAnalyzer project

Projects
1

this line: int average = sum / size.grades();

produces the following error:

GradeAnalyzer.java:20: error: cannot find symbol
int average = sum / size.grades();
^
symbol: variable size
location: class GradeAnalyzer
1 error

Although it is exactly written like that in the walk through video!
What is the problem!?

import java.util.ArrayList;

public class GradeAnalyzer{
  public GradeAnalyzer(){
    
  }
  public int getAverage(ArrayList<Integer> grades){
    if(grades.size() < 1){
      System.out.println("Sorry, the array list is empty! ");
      return 0;
    }
    else{
      int sum = 0;
      for(int grade : grades){
        sum += grade;
      
      }
      int average = sum / size.grades();
      System.out.println(average);
      return average;
    }
  }
  public static void main(String[] args) {
    ArrayList<Integer> myClassroom = new ArrayList<Integer>();
    myClassroom.add(98);
    myClassroom.add(92);
    myClassroom.add(88);
    myClassroom.add(75);
    myClassroom.add(61);
    myClassroom.add(89);
    myClassroom.add(95);
    
    GradeAnalyzer myAnalyzer = new GradeAnalyzer();
    
    myAnalyzer.getAverage(myClassroom);
  }
}
2

grades is an array list, size is an array list method, as you demonstrated here:

if(grades.size() < 1)

you know how tall call the size method on the array list, but for some reason you make a mistake in the line that produces an error