Time span calculation 6/10

Screen Link:
https://app.dataquest.io/m/497/date-and-time-manipulation-in-r%3A-fundamentals/6/time-span-calculations

My Code:

library(lubridate)
now <- Sys.time() %>% as_datetime
days_since_founding <- now - ymd_hms("2015-03-01 00:00:00")

What I expected to happen:

The course did not provide any context for “as_datetime”. Can you elaborate on this one?
Also I used :
now ← ymd_hms(Sys.time())
days_since_founding ← now - ymd_hms(“2015-03-01 00:00:00”)
Is this appropriate?
What actually happened:

Replace this line with the output/error