Yes, you are right! However, writing it as starting from 0 will just make us subtract a (6/5)^0 = 1 on the outside of the series to make up for our change in the start of the summation, and subtracting 1 from something divergent will leave us with something that is still divergent. So, in the end, the answer was still correct.
Ma'am, I thought you mentioned that the geometric series can be dealt with once we have it starting from zero instead...
Yes, you are right! However, writing it as starting from 0 will just make us subtract a (6/5)^0 = 1 on the outside of the series to make up for our change in the start of the summation, and subtracting 1 from something divergent will leave us with something that is still divergent. So, in the end, the answer was still correct.