A retrospective observational study which is used in medical and psychological research by checking historic records .
This study looks backwards in history to examine exposures to suspected risk or protection factors in relation to an outcome that is considered at the beginning of the study.
The given statement says that A statistical analyst obtains data about ankle injuries by examining a hospital's records from the past 3 years.
Hence, this is a retrospective observational study.
you can't solve x because it is 2 linear equation and you only have one equation