The impulse required to decrease the speed of the boat is equal to the variation of momentum of the boat:
[tex]J=\Delta p=m \Delta v[/tex]
where
m=225 kg is the mass of the boat
[tex]\Delta v=v_f-v_i=15 m/s-21 m/s=-6 m/s[/tex] is the variation of velocity of the boat
By substituting the numbers into the first equation, we find the impulse:
[tex]J=m\Delta v=(225 kg)(-6 m/s)=-1350 N s[/tex]
and the negative sign means the direction of the impulse is against the direction of motion of the boat.
