I have no idea about how to use two "enable inputs". (the second part of the question)
When neither of the enable inputs is asserted, all of the outputs are disabled.
If you're stuck on implementation, I advise you to study the 74LS137 3-to-8 decoder :)
Actually, since the question doesn't require address latches, it might be easier for them to study the 74xx138 IC. Good suggestion, though.
(xx = HC, AC, LS, whatever).
berkeman: you're quite right, ty
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