A lady bought a house at Ikate, Lekki for N60 Million three (3) years ago. She sold it last month to relocate for N85 Million. The exchange rate 3 years ago was N360/$ and now at the black market where she exchanged at is ~N720/$. If she had held the money in Dollars, she would have had $166,000. When she converted the proceeds of the sale to Dollar, it amounted to $118,055. The rental income of the property was N12 Million for the 3 years.

What's a Treasury Bill?
It's also known as T-Bills
When the government needs money on the short term (< 1 year)

The govt issues this note to the general public and you need a minimum of N50 million to buy directly from the government. (CBN)
That market is called primary market There is another market called secondary market.

Institutions crowdfund investments from as little as N100,000(minimum) from different players to purchase from CBN (N50 Million limit)

This is where you and I and other people who do not have N50 million YET buy from.