what is the 8th term of the geometric sequence with this explicit formula

Answer: 640 (B)
Step-by-step explanation:
The explicit formula
an = -5 × ( -2 )(n - 1) bearing in mind that n = 8
Therefore, putting n = 8 - 1, = 7
-5 × -2(7) raised to the power of 7
an = -5 × -128
= 640