[填空题]
A ball is thrown straight up with a spee f+ zpdsp01vp:2f-j5rjpjfu, d of 30 m/s. (o1q2jpe iyb:tg*rc:/ - (nio awnly fill in numerical value inwj2rqb - i/t:1 pgoci(eya:*n the blanks) (a.) How long does it take the ball to reach the maximum height? $s$ (b.) What is the maximum height reached by the ball? $m$ (c.) What is its speed after 4.2 s? $m/s$