hello :
the general term is : an = a1×r^(n-1)
a1 : the first term....( a1 = 6)
r : the common ratio......( r = -1/3 )
when : n = 8 a8 is the eighth term : a8 = 6×(-1/3)^7
a8 =- 6×(1/3)^7 because : (-1/3)^7 = - (1/3)^7
a8 = -2 ×(3/3^7)
a8 = -2×(1/3^6)
a8 = (-2)/[ 3^6 ]