I have an apple tree, which grows 5 new apples every 3 days. However, I pick an apple from the tree every day. Today, there are 10 apples on the tree. How many more days will it be before it has 40 apples?
In 3 days, the tree will have 5 more apples, but you will pick 3 of those apples.
So every 3 days you get 2 more apples.
We need 40-10=30 more apples on the tree.
It will be 45 days before your apple tree has 40 apples.