we have that
The equation of the given line is
y=1
this equation represents a horizontal line
so
the slope is zero (m=0)
Remember that, if two lines are parallel, then their slopes are equal
that means
the slope of the parallel line is m=0 too
step 2
Find out the equation in slope-intercept form
y=mx+b
we have
m=0
point (-1,3)
the equation is
y=3