This is a tough one! Could you let us know if you're applying to a W. African office? If not, there's quite a lot of difficult assumptions to make here.

That being said, here's how I'd go about this market sizing question:

What I know:

• Sierra Leone is in West Africa, and not that large, meaning it's population is probably between 5 and 10 million
• I thought West Africans generally eat flour-based food, but I would clarify whether rice was actually their staple (note, I googled this and confirmed that 85% of farmers cultivate rice)
• They have a fairly high % of the population that's poor, so rice, being the staple, would be heavily consumed
• When cooking, I use a cup of rice for every 3 people.

Now that I know what I know, I'll break this problem down.

8 million citizens times ~80% eating rice daily as their main source of nutrition = 6.4 million eating rice daily

1 cup of rice per person per day (I use 1 cup for 3 people as a side, so I'm assuming triple this to account for multiple meals and it being more of a base) = 6.4 million cups per day

6.4 million cups/day times 365 days/year = ~2.3 billion cups of rice a day

(Note: I would check if we need this calculation in servings or grams and adjust accordingly), meaning:

• 6.9 billion servings
• 460 trillion grams (~200 grams per serving)
• 460,000 tonnes (1,000,000 grams in a ton)

(edited)