Which itr applicable

Sir, my client is a worker in a shop at kolkata earn @ Rs. 6,000 /- pm. He has applied for bank loan for business purpose, now bank demand IT file for back 3 years. My question is that 1). How can he show his income and in which ITR form? 2). 2 years i.e 2014-15 & 2015-16 he can file but 2013-14 how he can file it? If he will file now for 2014-15 then any penalty will impose? Pls clarify me.