<prompt> Translate the following text to EnglishKama mshahara wa ziada umehesabiwa kwa usahihi na Profesa Wachter, itakuwa vigumu kutetea udhibiti wa posta ya Marekani kwa misingi ya kiuchumi tu.  <response>: If the wage premium is accurately calculated by Professor Wachter, it would be difficult to defend the U.S. postal monopoly on purely economic grounds. 