step 1
Find out the slope of the line
y=-x+5
the slope is m=-1
Remember that
If two lines are parallel, then their slopes are equal
so
the slope of the parallel line is m=-1 too
step 2
Find out the equation of the parallel line
y=mx+b
we have
m=-1
point (-2,3)
substitute and solve for b
3=-1(-2)+b
3=2+b
b=1
therefore
the answer is
y=-x+1