Solution:(b) Anshul said to me, "My mother is not at home. She will be back tomorrow." (Correct)(a) Anshul said to me, "My mother was not at home. She will be back the following day. (Change of reported speech to simplepast and also the following day is incorrect)
(c) Anshul said to me, "My mother is not at home. She would be back the following day" (Incorrect tense & also the following day is incorrect)
(d) Anshul said to me, "His mother was not at home. She would be back tomorrow." (Incorrect tense)