Vector A has a magnitude of 23 units and points in the positive y-direction. When vector B is added to A, the resultant vector A+B points in the negative y-direction with a magnitude of 15 units. Find the magnitude of B?

Question

Vector A has a magnitude of 23 units and points in the positive y-direction. When vector B is added to A, the resultant vector  A+B  points in the negative y-direction with a magnitude of 15 units. Find the magnitude of B?