Draw the condensed structural formula and give the IUPAC name for each of the following:
a. a carboxylic acid that has the formula $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}$, with no substituents
b. a carboxylic acid that has the formula $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{2}$, with one ethyl substituent