I’m a bit stuck on this simple question.

Question

So the values I’ve got:
Propellant = 100,000 kg
Structure = 10,000 kg
Payload = 5000 kg
So I worked out:
Propellant fraction is 87%
Payload fraction is 4.3%
Now I need to find
“Recall the relationship between specific impulse and exhaust velocity is given by V=gI (Where g = 9.81 and I = 450). What is the change in Velocity (V)in m/s this rocket will produce if all the propellant is consumed in one stage?”
I have tried to work this out and arrived at 1436 m\s but I don’t think I am correct.
Any advice?
Many thanks