Final answer:
To achieve a resultant vector of 15 km east, you must add a 5 km vector pointing east to the existing vector of 10 km east.
Step-by-step explanation:
The question is asking which vector needs to be added to a vector cv of 10 km, pointing east, to result in a resultant vector of 15 km, also pointing east. Since vectors in the same direction add up by simple arithmetic, you would add a vector of 5 km pointing east to the original vector cv. They follow specific rules for addition. In this case, we're essentially thinking of 'west' as negative and 'east' as positive. The head-to-tail method is used here.The sum of the two vectors (10 km + 5 km) is a resultant vector of 15 km, pointing east.