a. There are two functional groups in this compound, carboxylic acid and keto group. Out the two carboxylic acid has higher preference, so the numbering starts from carboxylic carbon.

b. There are 5 carbons in the parent chain hence the parent name pentanoic acid.

c. The keto group is at 4^th carbon. When keto group does not get the first preference it is prefixed as –oxo-. Hence the name 4-oxo-pentanoic acid.