Vof magnitude 100 and direction 172 degrees, and w of magnitude 300 and direction 310 degrees, find v+w

From the attached diagram, we can see that the vector v and vector w form a triangle with an angle of 310-172=138 degrees

Since the vector v+w is the opposite of angle 138 degrees, we can use cosine rule to find the size of vector v+w

Answer: c. x y2 04 66 16