automata is an interesting and at the same time a tough subject if u want to genuinely acquire sound knowledge of it.It is an important part of competitive xams like GATE etc.. plus if u want to opt for higher studies knowledge of automata is essential... for WBUT purpose solving mishra chandrasekharan and last five yrs questions will b more than enuf... however if u want to go for higher studies u must refer to books like hopcroft ulmaan/martin/sipser etc after going thru mishra chandrasekharan