We Know, P = m*v
Here, m = 30 Kg
v = 5 m/s
Substitute it into the expression,
P = 30*5 Kgm/s
P = 150 Kgm/s
So, your final answer is 150 Kg.m/s
Hope this helps!
The displacement ........................
I added individual steps for clarity. Note that g must be positive if the solution is to be real.

Let me know if you have any questions.
Vf = Vo + at
Vf = 20 m/s
Vo = 50 m/s
a = ?
t = 15
Therefore
20 = 50 + 15a
20 - 50 = 15a
-30 = 15a
a = -30 / 15
a = -2 m/s²