A= (-3, -4) and B= (-2,j). if B is in the second quadrant and is perpendicular to A, what is j to one decimal place?

Assignment Question
A= (-3, -4) and B= (-2,j). if B is in the second quadrant and is perpendicular to A, what is j to one decimal place?
Solution:
A=(-3,-4)
B= (-2,j)
Given ). B is perpendicular to A
=0
After matrx multiplication
But B is in second quadrant so

j to one decimal place=...