So first Identify all the given Varibales so u can choose which Eqauton to use
D=200m
T=4s
Vi=10m/s
Vf=?
You should this equation
D= 0.50(Vf+Vi)T
Plug in the values
200= 0.50 (Vf+10) 4
Divide the 4 out of the right side and if you do sumthing to one side you gotta do it to the other
200 divided by 4= 0.50(Vf+10)
50= 0.50(Vf+10)
Now expand the 0.50
So 50= 0.5Vf + 5 (because 0.5 times 10 is 5)
Now get rid of the 5
50-5= 0.5Vf
45 =0.5Vf now Divide the 0.5 out
45 divided by 0.5 = Vf
And 45/0.5 is 90
So 90=Vf
Therefore the final Velocity is 90m/s