SOLUTION
The following is a geometric series
We will use the formula

Where Tn is the nth term of the series,
n is the number of terms = 8,
a is the first term = 15
And r is the common ratio = 1.2 (to find r, divide the second term, 18 by the first term which is 15
Now let's solve

So the 8th term = 53.748