I assumed an emulator was intended...
And yeah, the FX-82 doesn't seem like a good example, i.e., it's a trivial solution. Surely a "four banger" was intended as the "simple calculator", and the graphing calculator is the goal?
Mind, they're not asking so much for a solution, as a method of solution.
For example:
- What CPU is in the original calculator?
- Can it be programmed at all? Does it use mask ROM? (If so, then no!) Does it have an external ROM chip, or cartridge, or [executable] RAM? Also, how much memory space does it even have? It might not be able to run such a complicated program at all, even if it can be programmed.
- If not, you must replace the CPU, or PCB, with one that can.
- Once you have a programmable platform, you must write the program. This... would be extremely lengthy to do from scratch, and prone to errors, especially if you don't have any experience with programming of embedded devices, and structured programming in high-level languages.
- So what can you do about that? Well, a more likely approach is to find some off-the-shelf libraries, and either port them to your platform, or create an interface (or even an emulator) that runs on your system that can work with the existing libraries (because, maybe you can only find binaries, or libraries, but not the source?).
- Somewhere along the way, you need to figure out how to change the numbers and a couple operator keys into a full scientific (and graphing) keypad. There aren't nearly as many keys as a graphing calculator has, so you need to encode operations as key combinations or sequences. (Scientific calculators already have a shortage, hence the "2nd function" key on most of them! You could take the same mechanism, but vastly expand it, to make better -- and, unfortunately, far more cryptic -- use of the few keys you have.)
This is probably far too much, far too useful, information than I should provide under the circumstances. Perhaps your employer will at least read the subtext that you are at least able to look up answers online...
Also, for your own purposes -- because, remember, an employment is a relationship, and that goes both ways -- if your potential employer is asking about, essentially, hacking and reverse- and forward-engineering embedded devices -- how relevant is that actually to the expected duties of this position?
Is the job description itself actually representative of what's going on? For example, you might be responsible for such-and-such technical tasks, but it ends up being a bunch of stupid paperwork and office politics because it's a large and entrenched corporation with that kind of culture. (In which case, that may still be an okay job, at least for a while, but you will soon come to appreciate why the Dilbert comic remains as popular as it is...)
Tim