A student prepares an aqueous buffer solution containing propanoic acid, \(\text{CH}_3\text{CH}_2\text{COOH}\) (\(\text{p}K_a = 4.87\)), and sodium propanoate, \(\text{NaCH}_3\text{CH}_2\text{COO}\). The measured \(\text{pH}\) of the buffer solution is \(5.50\). Which of the following correctly compares \([\text{CH}_3\text{CH}_2\text{COO}^-]\) and \([\text{CH}_3\text{CH}_2\text{COOH}]\) in the solution, and provides the correct justification?