Answer: A) it is not grammatically correct.
Explanation: From the given options, the one that represents what is wrong with the given sentence, is the corresponding to option A: it is not grammatically correct, it has two grammatical errors, the first one is that it should say "I am interested" because "interested" is the participle of the verb interest. The second error is that the pronoun "you" should be replaced for "your" because it is indicating belonging, so the correct sentence would be: I am interested in applying for the position of cashier at your business.