To find out how many students are in Charlie's class, you can divide the total number of ghost cookies he decorated (84) by the number of cookies each student gets (4).
Start with the total number of ghost cookies Charlie decorated, which is 84.
Now, you want to figure out how many students are in the class. Let's call this number "S" for students.
Since each student gets 4 cookies, you can set up an equation: 4 cookies per student x S students = 84 cookies.
To solve for S (the number of students), divide both sides of the equation by 4:
(4 cookies per student x S students) / 4 = 84 cookies / 4
When you divide both sides by 4, you get:
S students = 21
So, there are 21 students in Charlie's class. Each student gets 4 ghost cookies for the Halloween party.