Plz explain faster please

Dear Student
The initial velocity of the ball, u = 15 m/s
the final velocity of the ball, v = 0
Using the equation of motion:
$$\begin{gathered} v^2=u^2-2gh \\ \Rightarrow 0={15}^2-2\times 9.8\times h \\ \Rightarrow h=\frac{225}{19.6}=11.48 \text{m} \end{gathered}$$
Time taken 
v = u - gt
0 = 15 - 9.8 t
t = 15/ 9.8  = 1.530 s

Regards