Answer is 120.
(Sorry if photo quality is bad. The camera on my device sucks.)
Answer:
The -1 came from factoring.
The equation is multiplied by 8 because 8 could be pulled from 16x-8.
16 can be divided by 8 2 times and 8 can only divided by 8 once.
so factoring it makes the equation 8(2x-1)
X = 12, because there is only one answer that has a number bigger than 9 :)