This simple answer is worth full marks. Several students came up with this answer in the exam. Several more produced answers which were close to it. Of course, this was intended to be the "putting it all together" question and I was not surprised that many students left it blank.
There are other possible approaches, but none of them are this simple.
In practice, we probably wouldn't want to design the circuit like this because we would probably have to use a large number of commercial EPROM chips to work this way. A typical EPROM does not have these hundreds of output lines.