Two lines are parallel when they have the same slope.
Isolating y from 5x-3y = -6, we get:
5x - 3y = -6
5x - 3y - 5x = -6 - 5x
-3y = -6 - 5x
-3y/(-3) = (-6 - 5x)/(-3)
y = -6/(-3) + -5x/(-3)
y = 2 + 5/3x
the slope of this line is 5/3, then it's parallel to y= 5/3x-8