Vector vector A has a magnitude of 27 units and points in the positive ydirection. When vector vector B is added to vector A , the resultant vector vector A + vector B points in the negative ydirection with a magnitude of 18 units. Find the magnitude of vector B ?
1 answer

Since both is in yaxis (+ and ) you can use the magnitude of the resultant as the sum of the magnitudes of the two vectors A and B. (from Maazul H)
A= 27 units
B=?
A+B= 18 units ( yaxis)
27+B= 18 units (+ yaxis)
B= 1827
B= 45
The magnitude of vector B is 45 units