Those sprockets are fairly worn, but not as bad as many we see. Whatever you do, don't replace a chain or sprockets without replacing the mating parts: replace a set of meshing parts or keep using the old ones. If you clean your chains properly, then keep them clean and oiled, in normal suburban mowing you may get a number of years out of those sprockets and chains. Just remember, degrease and re-lubricate the chains regularly. When you can see or feel just a bit of grittiness on the inside of the chaincase cover, it is time to service the chains again. By keeping the inside of the chaincase as clean as the chains, it is easier to tell when some grit has got in. By persevering with those fairly worn ones, you can learn good maintenance habits without risking an expensive set of new parts.
