Rational Number are set of numbers that can be written as a/b where a and b are integers, but b is not equal to 0; an integer or a fraction; for example: 6 can be expressed as 6/1 and 0.5 can be expressed as 1/2.
I think you are correct actually.
Sn=sum of the n terms of the geometric sequence.
a= the first term
r=the common ratio
n=numbers of terms.
Sn=a[(1-r^n)/(1-r)]
In this case:
a=-3
r=a₂/a₁=15/-3=-5
n=9
S₉=-3[(1-(-5)⁹) / (1-(-5))=
S₉=-3(1+1953125)/6)=
S₉=-3(1953126/6)=
S₉=-3(325521)
S₉=-976563
Answer: A. -976563
