How did Mansa Musa become rich?

Mansa Musa inherited a kingdom that was already wealthy, but his work in expanding trade made Mali the wealthiest kingdom in Africa. His riches came from mining significant salt and gold deposits in the Mali kingdom. Elephant ivory was another major source of wealth.

answer; i believe the correct answer is (a) nigeria is the largest african crude (oil) supplier; /// so revenue from petroleum;

all fossil fuels are nonrenewable, so think coal, gasoline, things that we will eventually run out of. all fossil fuels are nonrenewable resources, but not all nonrenewable recourses are fossil fuels. these resources are not being renewed as fast as we are using them. i hope this considering there weren't any answer choices.