Answer:
t = 2.52 seconds
Step-by-step explanation:
h=139-15t-16t^2
We want to know when the ball hits the ground
That would be when h=0
0 = 139-15t-16t^2
We can use the quadratic formula to find t
t = -b ± sqrt(b^2-4ac)
        ----------------------
           2a
where a = -16   b = -15  and c = 139
 t = -(-15) ± sqrt((-15)^2-4(-16)139)
        ----------------------
           2(-16)
 t = (15) ± sqrt(225+8896)
        ----------------------
           -32
t = (15) ± sqrt(9121)
        ----------------------
           -32
t = 15+ sqrt(9121)                       t = 15- sqrt(9121)
      --------------------   or                    -------------------  
            -32                                               -32
         -3.453247707        or              2.515747707
Since time cannot be negative
  2.515747707
Round to the nearest hundredth
t = 2.52 seconds