for If I had 90 candies and I had to take 4 candies a day for 30 days how much candy would I have left after the 30 days is up
After 30 days you wouldn't have any candies left.
You would have eaten the last of your candies on the 23rd day.
22 days at 4 candies/day = 88 candies
The last two candies get eaten on day 23,