Answer:
On the 6th mailing there are 4096 letters
Explanation:
A geometric sequence is given by
an = a1 *r^(n-1)
Where a1 is the first term and r is the common ratio (what we multiply by each time) and n is the term number
The first person has mails 4 letters so a1 =4
Each person sends 4 so the common ratio is 4
We are finding the 6th mailing
a6 = 4 (4) ^ (6-1)
a6 = 4*4^5
a6 = 4096