Initially, the body starts its motion from rest therefore, u=0. 
Velocity v,  when the object falls for 5 seconds before acceleration due to gravity is ceased:
v=u+at
  =0+9.8×5=49m/s

Just before the acceleration stops acting the velocity of the body is 49m/s. 
Now the distance travelled by the body in the next 3s
Now, g= 0 m/s

$\mathrm{s}=\mathrm{ut}+\frac{1}{2}{\mathrm{gt}}^2$
= $49\times 3+\frac{1}{2}\times 0\times {\mathrm{t}}^2$  
= 49 x 3 = 147 m