i) The domain and range of inverse functions are swapped. So swap the x and y values.
ii) A function only has an inverse if it's one-to-one. The easiest way to tell if a function is one-to-one is to graph it and draw horizontal lines through it. If any of the horizontal lines do not touch the graph or touch the graph at more than one point, then the function is not one-to-one and can not have an inverse.