Final answer:
The relative speed of the Green plane to the Yellow plane is the sum of their speeds because they are moving in opposite directions, resulting in a relative speed of 267 km/h.
Step-by-step explanation:
The speed of the Green plane relative to the Yellow plane is calculated by combining the speeds at which they are both travelling, since they are moving in opposite directions. The Green plane is traveling north at 100 km/h, while the Yellow plane is traveling south at 167 km/h. To find the relative speed, you add their speeds together, because they are moving in opposite directions.
The relative speed of the Green plane with respect to the Yellow plane is:
100 km/h + 167 km/h = 267 km/h.
Therefore, the answer is (a) 267 km/h.