I = 7 N-s
Explanation:
Impulse is defined as
I = ∆p = m(vf - vi)
We are given
m = 0.2 kg
vi = -10 m/s (to the left)
vf = +25 m/s (to the right)
Therefore, the impulse imparted on the puck is
I = (0.2 kg)[25 m/s - (-10 m/s)]
= (0.2 kg)(35 m/s)
= 7 N-s