Consider the ground surface as Zero.
Since the capsule was buried 1.8 meter below the ground it would be a negative number ( below zero is negative) so the capsule is -1.8 meters.
The sign was buried 1.2 meters above the capsule, so the given equation -1.8 + 1.2 = -0.6 shows that the sign is 0.6 meters below the ground.
The answer is B.