35517

For this question you have to observe the word and see what happens to the word each time it goes through a box.
I noticed that each time the word went through a box it had one less letter at the beginning of the word each time.Also it still became another word even though a letter was taken away from it each time.
However when the word goes through the last box the last letter of the word is taken away instead of the first letter in order for the output to still be a word.
Lastly I've noticed that there are 4 boxes and the word is 5 letters long so in order for this to work the word you put in must be a 5 letter word so that the last box gives out a letter which is also a word.
The word that I chose to put in the box was cheat because it has the same letters as the word wheat apart from the first one but it still works.