Two Satellites with Equal Rest Masses of 100 Kg Are

Multiple Choice

Two satellites with equal rest masses of 100 kg are traveling toward each other in deep space. They have identical speeds of 0.600c. The satellites collide and somehow manage to stick together. What
Is the rest mass of the combined object after the collision?

A) 225 kg
B) 275 kg
C) 300 kg
D) 250 kg
E) 200 kg