for question 27)
since the total time of flight is 2.5s, 1/2 flight is 1.25s
using the vertical acceleration forumla: y' = v - 9.8 t
we know at max height y' = 0, and this occurs at 1.25s
so 0 = v - 9.8 (1.25), v = 12.25 m/s
sub into y = vt - 4.9 t^2, with t = 1.25 and v = 12.25 you get...