Answer
On the seventh day, 93,312 mails need to be sent.
Step-by-step explanation
This question has a setup of a geometric progression.
The general form of a geometric progression is
aₙ = a rⁿ⁻¹
where
aₙ = nth term
a = first term = 128
r = common ratio = 3
n = number of days
So, for this question,
aₙ = a rⁿ⁻¹
aₙ = 128 (3ⁿ⁻¹)
On the first day, n = 1
aₙ = 128 (3ⁿ⁻¹)
a₁ = 128 (3¹⁻¹)
a₁ = 128 (3⁰) = 128 (1) = 128
On the seventh day, n = 7
aₙ = 128 (3ⁿ⁻¹)
a₇ = 128 (3⁷⁻¹)
a₇ = 128 (3⁶) = 128 (729) = 93,312
Hope this Helps!!!