we have that
The line passing through (1,y) and (3,0) is perpendicular to the line joining (5,3) and (-1,1)
step 1
find the slope of the line joining (5,3) and (-1,1)
slope m=(y2-y1)/(x2-x1)----> m=(1-3)/(-1-5)---> m=-2/-6---> m=1/3
step 2
if two lines are perpendicular
the slopes
m1*m2=-1
m1=1/3
m2=-3
so
The line passing through (1,y) and (3,0) has a slope m2=-3
m2=(y2-y1)/(x2-x1)----> m2=(0-y)/(3-1)----> -y/2
-3=-y/2----> y=6
the answer is
y=6