A 15.0 kg penguin is walking south at a speed of 7.0 m/s when it collides with another penguin of mass 10.0 kg that is stationary. After the collision, the 15.0 kg penguin moves at a velocity of 4.2 m/s 20 degrees east of south. What is the velocity of the 10.0 kg penguin after the collision?
a. 2.1 m/s, 20 degrees west of south
b. 5.0 m/s, 20 degrees east of south
c. 7.3 m/s, 20 degrees west of south
d. 4.2 m/s, 20 degrees east of south