The momentum of a moving object is given by:
[tex]p=mv[/tex]
where m is the mass of the object and v its speed.
In this problem, the ball has a mass of [tex]m=6 kg[/tex] and its momentum is [tex]p=72 kg m/s[/tex], so we can rearrange the previous equation to find the speed of the ball:
[tex]v= \frac{p}{m}= \frac{72 kg m/s}{6 kg}=12 m/s [/tex]
