Think of the given points as endpoints of vectors.
The point (3, 1) is the terminus of the vector 3 i + j.
The point (-4, 2) is the terminus of -4 i + 2 j.
By the "triangle rule" for vector summation, the vector starting at (3, 1) and ending at (-4, 2) is the difference between these two vectors.
(-4 i + 2j) - (3i + j) = -7 i + j
