While 'more than' may have been the correct answer in the past, 'more than' and 'over' are now considered interchangeable in relation to numerical values.

From the Grammarly Blog:   

>According to the AP Stylebook, “more than” and “over” can now be used interchangeably to indicate greater numerical value, and “less than” and “under” can be used interchangeably to indicate lesser numerical value. Prior to the rule change, the only acceptable use of “over” was as a locative...

  https://www.grammarly.com/blog/synonymizing-more-than-and-over/