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 60 ft from​ you?

Answer 1

$$100-20t=60$$

$$20t=40$$

$$t=2$$

Or

$$100-20t=-60$$

$$20t=160$$

$$t=8$$

She is 60 ft from​ me after $2$ seconds or after $8$ seconds.