The expression 8x2 − 144x + 864 is used to approximate a small town's population in thousands from 1998 to 2018, where x represents the number of years since 1998. choose the equivalent expression that is most useful for finding the year where the population was at a minimum.
8(x2 − 18x + 108)
8(x2 − 18x) + 108
8(x − 9)2 − 216
8(x − 9)2 + 216