Answer:
20 mail
Step-by-step explanation:
If we observe the progression of the sequence, we will see that the number of mail for the next month is gotten by adding the next odd number to the previous month's number of mail (1, 3, 5...).
To get for January, 5, 1 was added to 4.
To get for February, 8, 3 was added to 5.
To get March, 13, 5 was added to 8.
Therefore, to get for April, we add the next odd number to 13, i.e.
13 + 7 = 20
Hence, Arjun will send 20 mail in April.
