What were the initial circumstances that led Cholkar to make a vow to Sai Baba?

Chapter 15 describes Cholkar's difficult situation which prompted his vow. He came from a "poor household" where everything depended on his job. To make his salary permanent, he was required to pass an examination. The stakes were incredibly high, as failing the exam meant that "even his daily bread was at stake and his candidacy would go." Faced with this pressure, he made a firm resolve, vowing to Sai Baba that if he passed the exam by Baba's grace, he would present himself at Shirdi and distribute sugar candy in Baba's name.