Hello,

You can break this question up into two parts:
1) how long it takes the projectile to reach its maximum height and then fall back to its original level in the vertical dimension
2) how long it takes the projectile to subsequently fall an additional 25m


Part 1:

vi = 40sin30
vf = 0
a = -10

use t = (vf-vi)/a to find how long it takes the ball to reach its maximum height. then double this time to get how long it takes the ball to fall back to it's original position.

part 2:
now, you need to take into account the extra 25 m that the ball is elevated. the values we have now are:

vi = -40sin30
a = -10
y = 25 m

use y = vf*t - (a*t^2)/2 and solve for time.

add this time to get the total time of the projectile in the air.

Hope this helps