Answer:
I can not see the table, so i will answer this in a general way.
Ok, let's see a rough image of what is happening.
First, Joey sends the email to 2 friends.
So first, 2 people have the email
Then each friend sends the email to 3 new people.
So now the number of people that has the email is:
2 + 2*3 = 2 + 6.
Now, the 6 new people that received the email send it to other 3 new people each, so now the number of people that got the email is:
2 + 6 + 6*3
and so on.
We already can see the pattern here, we can write this as:
∑aₙ
Where aₙ = 3*aₙ₋₁
and a₀ = 2.
So with that information, we can find the number of iterations, n, for a given number of people that received the email A.
A = ∑aₙ = (a₀ + a₁ + a₂ + ....) = (2 + 2*3 + 2*3*3 + ...)
