Error caused in mutate function (mask$eval_all_mutate())

Don't know if I'm getting the syntax wrong or not. I've already downloaded the dplyr package and tidyverse package.

The code below is what I wrote:

Watch_time_hour <- mutate(twitchdata,Watch_time_hours == Watchtime(Minutes)/60)

Below is the error message I get from typing in this code.

Problem while computing ..1 = Watch_time_hours == Watchtime(Minutes)/60. Caused by error in mask$eval_all_mutate(): ! object 'Watch_time_hours' not found