Two displacements, one with a magnitude of 15.0 m and a second with a magnitude of 20.0

Question:

Two displacements, one with a magnitude of 15.0 m and a second with a magnitude of 20.0 m, can have any angle you want.
(a) How would you create the sum of these two vectors so it has the largest magnitude possible? What is that magnitude?
(b) How would you orient them so the magnitude of the sum was at its minimum? What value would that be?
(c) Generalize the result to any two vectors.