Answer:
y = -x - 2
Explanation:
Note that the given line, y=-x+3, has a slope of -1. Any new line parallel to this one must also have that slope, -1:
y=-x+3 becomes 3 = -(-5) + C, where C is the y-intercept:
3 = 5 + C, or C = -2
Thus, the desired equation of this new line is y = -x - 2