need help finding percent change

\begin{tabular}{|l|l|l|l|} \hline & 2021 & 2020 & Percent Change \\ \hline Accounts receivable & 4,849,000,000 & 4,938,000,000 & \\ \hline Allowance for doubtful accounts & 189,000,000 & 233,000,000 & \\ \hline Allowance for doubtful accounts at a percentage of A/R & 3.89% & 4.71% & \\ \hline \end{tabular}