Afootball is kicked into the air from an initial height of 3 feet. the height, in feet, of the football above the ground is given by s(t)=-16t^2+35t+3.
where t is time in seconds and t> =0. which is closest to the time when the football will be 20ft above the ground? ?

a) 2.72 seconds
b) 0.73 seconds or 1.46 seconds
c) 0.53 seconds
d) 0.53 seconds or 2.72 seconds

 For this case we have the following quadratic equation:
 
 Where,
 t: time
 s: height of the ball
 By the time the height is 20 feet we have:
 
 Rewriting the polynomial we have:
 
 Using the quadratic formula we have:
 
 Substituting values we have:
 
 Doing the calculations we have the roots are:
 
 
 the time when the football will be 20ft above the ground is:
 B) 0.73 seconds or 1.46 seconds