Hi there!
We can begin by breaking the problem up into two directions, horizontal and vertical.
The collision is perfectly inelastic since the two objects stick, so:
1 = car
2 = truck
Momentum in the east direction (positive and horizontal, car NOT going in this direction has a velocity of 0 m/s):
m2v2 = (m1 + m2)v
(650 · 11) / (350 + 650) = 7.15 m/s
Momentum in the north directions (only initial is the northward velocity of the car):
m1v1 = (m1 + m2)v
(350 · 16)/(350 + 650) = 5.6 m/s
Find the overall velocity using the pythagorean theorem:
√(5.6²) + (7.15²) = 9.08 m/s
Find the direction using trigonometry. Use tangent in this situation:
tan Ф = O/A
tan⁻¹(5.6/7.15) = 38° north of east