Snall in the well problem

Question

I can't understand snell in the well ,plz understood me instead of giving the solution.

Plz explain the relation between depth and the days.
And plz explain everything of that .

Answer 1

And when the sum reaches to the input given or greater than the input break the loop

Answer 2

a snail can only crawl out of a well during the day. it crawls 7 feet a day. if it has not crawled the entire length of the well, it descends 2 feet at night. and a new day begins again

Answer 3

.

Everyday the at day it is climbing 7 feet so make a variable sum for the summing the feets in a day and at night it is also coming 2 feet back so at each iteration subtract the sum by 2.