the deflnn is

y = ut + ( 1 / 2 ) a t ²  = ( 1 / 2 ) a t ² 

to find t =  ( s / v ) = 100 m./  270 m/s = 10 / 27 s  ( assuming uniform in this )

to find a , we know here

F= q B v

ma = q B v  =>   a =  q B v / m

so

y = ( 1 / 2 ) ( q B v / m ) ( s / v ) ²

plug the values. result should come.