First let us see what in formation we have:

s - Displacement - 50 metres

u - Initial velocity - 30m/s

v - Final velocity - N/A

a - Acceleration - 9.8m/s

t - Time - ?

We will take all values as downward, that is why we have acceleration as a positive value.

From the above information you should notice that we can use the following formula

Subbing in our values gives us,

Which is just a normal quadratic.

Hope this helps

Craig