Original Text
For the moon alone the days amount in 3 years to 1062 days, and in 5 years she falls 50 days behind: [i.e. to the sum (of 1770) there is to be added (1000 and) 62 days.]
Simple English
The moon's days total 1062 over 3 years, and in 5 years, it lags behind by 50 days.