A 3.9 g bullet leaves the muzzle of a rifle with a speed of 311 m/s. What total constant force is exerted on the bullet while it is traveling down the 0.82 m long barrel of the rifle?

I converted 3.9 g to .0039 kg
Used the equation t=d/r (.82m/311m/s)=.0026s

then a=v/t (311 m/s/.0026s)=119615 m/s^2

then multiplied this by the mass but I got it wrong. I'm not sure where I went off track

Realized I was using the wrong equation! Figured it out so never mind this one =)