This west african country has the greatest population on the entire continent and is also a member of opec.

I believe the answer is: Nigeria
Despite having a large amount of oil resources, Nigeria currently facing a big problem due to an over attachment to the oil sector as their most dominant source of economy.
Which means that the rate of inflation and unemployment in Nigeria is heavily influenced by the world's oil price.

Fiscal policy because it refers to the use of government spending and tax policies to influence macroeconomic conditions, including aggregate demand, employment, inflation, and economic growth.