we have that
x-y=3 -------> equation 1
and
ax+3a=0------> equation 2
we know that
ax+3a=0-------> a*(x+3)=0
a=0 and (x+3)=0
if a is a nonzero number
then
only
x+3=0------> x=-3
substitute the value of x=-3 in the equation 1
x-y=3------> (-3)-y=3-----> y=-6
the system has one solution-------> the point (-3,-6)
