Parallel lines have the same slope.
y = -1/2 x -3 has a slope of -1/2, so the new line has the same slope.
This gives us: y = -1/2 x + b
To find b, substitute in the given point (4,-1):
-1 = -1/2 (4) + b
-1 = -2 + b
1 = b
The new line is y = -1/2 x + 1.