Answer:
Number of groups formed by '<em>p</em>' people = 
Number of groups formed with 28 people = 7
Step-by-step explanation:
We are given that, there are 4 people in 1 group.
Now, at first we have to find the number of groups formed by '<em>p'</em><em> </em>people.
Here, we will use the unitary method.
Number of group formed with 4 people = 1
So, number of group formed with 1 person = 
∴ number of groups formed with '<em>p'</em> people = 
So, the required expression for the number of groups formed by '<em>p</em>' people is 
Now, secondly we have to find the number of groups formed by 28 people.
As, we know that number of groups formed with '<em>p</em>' people = 
Now, putting '<em>p'</em> = 28 in the expression obtained above, we get
number of groups formed by 28 people = 
So, there are 7 groups formed with 28 people.