So to do this, you need to rewrite $$x - 6y + 4$$ into a form where you can easily find the slope ($$y = mx + b$$). Once you have the slope, you'll have to set up $$y = mx + b$$ again, with the $$m$$ you found above, and plugging in $$\sqrt{x + 1}$$ for $$y$$, so $$\sqrt{x + 1} = mx + b$$, with $$m$$ from the previous step, and solve for b.