Audio power amplifier (output stage) class AB design?

i have been assigned to design an AB class audio power (for the final project of a basic course in electronics)amplifier using Opamp : 741 , power transistors BD137,138 , a 12 v. supply , load resistance 8 ohm , voltage gain of 40 dB and cut-off frequency 20 Hz. desperately needing help ! where shall i begin?!
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