expr1 = Eq(x * y - 20, 15 * y)
expr2 = Eq((x - 3) * y - 20, 15 * y)
expr3 = Eq((x - 6) * y - 20, 15 * y)
ranges = (x, 15, 30), (y, 0, 50)
p1 = plot_implicit(expr1, *ranges, adaptive=True, depth=0,
    label="adaptive=True, depth=0", grid=False, show=False)
p2 = plot_implicit(expr2, *ranges, adaptive=True, depth=1,
    label="adaptive=True, depth=1", grid=False, show=False)
p3 = plot_implicit(expr3, *ranges, adaptive=False,
    label="adaptive=False", grid=False, show=False)
(p1 + p2 + p3).show()