the expression 8x2 − 64x + 720 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.
a). 8(x − 4)2 + 592
b). 8(x − 4)2 − 592
c). 8(x2 − 8x + 90)
d). 8(x2 − 8x) + 90