Answer:
the final speed after attack is 69.09 km/h
Step-by-step explanation:
lion weight = 173 kg
running northward at 82.7 km/hr
weight of gazelle = 36.2 kg
running eastward at 57.4 km/hr
using momentum conservation along north direction
(173) × (82.7) = (173 + 36.2 ) × vₙ
vₙ = 68.38 km/h
using momentum conservation along east direction
36.2 × 57.4 = (173 + 36.2 ) × vₓ
vₓ = 9.93 km/h

hence the final speed after attack is 69.09 km/h