Solve x4 − 7x2 − 18 = 0

Asalesperson earns $320 per week plus 8% of her weekly sales. the expression representing her earnings is 320 + 0.08x. which of the following describes the sales necessary for the salesperson to earn at least $1000 in the one week?

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

15/16 as a decimal rounded to the nearest hundredth