I am stuck at how the answers for time were done. Which mathematical method was used to solve: -4.9t^2+5.14t-1.0=0 to get these values t=0.258s and 0.791s

' 12. A child is trying to throw a ball over a fence. She gives the ball an initial speed of8.0 f 40 above the horizontal. The ball leaves her hand 1.0 m above the ' as the fence while still traveling , How far is the child from the ground and the upwards and experiences no signi @ fence? 1 .6 m