Question 1183349
for only 3 months, doing it the way you did it is fine.
the second option is also a geometric progression type formula.
in that formula:
An = A1 * r ^ (n-1)
in your problem:
A1 = 30,000
r = 1.2
n = 3
you get:
A3 = 30,000 * 1.2 ^ 2 = 
there is also the sum formula that says:
Sn = A1 * (1 - r^n) / (1 - r)
in your problem:
n = 3
r = 1.2
A1 = 30,000
you get:
S3 = 30,000 * (1 - 1.2^3) / (1 - 1.2)
solve for S3 to get:
S3 = 109,200.


the formula is called a geometric sequence formula.
here's a reference.


<a href = "https://www.mathplanet.com/education/algebra-2/sequences-and-series/geometric-sequences-and-series" target = "_blank">https://www.mathplanet.com/education/algebra-2/sequences-and-series/geometric-sequences-and-series</a>