Answer:
.
Step-by-step explanation:
According to conservation of momentum, the momentum of rifle before fire is equal to the momentum of bullet after fire plus momentum of rifle after fire.
This in mathematics translates to.
![(M+m)v_(rifle-before-fire)=Mv_(rifle-after-fire)+mv_(bullet)](https://img.qammunity.org/2021/formulas/physics/high-school/zd00b2sq6jcin59mly4bploc39cauhc6qx.png)
rifle is stationary before fire so
this means that left side is 0.
![0=Mv_(rifle-after-fire)+mv_(bullet)](https://img.qammunity.org/2021/formulas/physics/high-school/v3m46urx2v0rfpbswruga0db5mo4zz5k6m.png)
solving for
in above gives us our answer.