I think the 80 represents how far away they initially start from you
And the 5 is their speed
d=|80-5t|
60=|80-5t| |square both sides
60² = (80-5t)(80-5t)
3600 = 6400-400t-400t +25²
25t²-800t +6400 =3600
25t² -800t + 2800=0
5t² -160t +560=0
(ax²+bx+c=0)
(a=+5 b=-160 c=+560)
Sub into -b formula
x=(-b±√(b²-4ac))/(2a)
t= (-(-160)±√((-160)²-4(5)(560))/(2(5)) .
Should get t=4 seconds and t=28 seconds
sub both values back in to make sure
d=|80-5(4)|
d=|80-20|
d=60ft
d=|80-5(28)|
d=|80-140||
d=60ft
