Question

Starting from 100 ft​ away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ​ft/s. Her distance d from you in feet after t seconds is given by d=|100-20t|. At what times is she 80 ft from​ you?

Answer 1

|100-20t| = 80
100-20t = ±80
20t = 100±80
t = 5±4
t = 1 or 9