This would be oil. Oil is a topic that has been hotly debated as it needs to be replaced by renewable alternatives such as wind or solar power for example. However, with the rise of the automobile industry and the industrial revolution in the late 19th century, and especially since the beginning of the 20th century, oil has been playing an ever-increasingly important role. This enabled economies in the Middle East to grow through oil sales.
3+6=9
15-9=6
9+6=15
I hope this was helpful have a good day! <3
D. Urban cities due to human population/activity
Don't quite follow this one but it looks like ...
m-2.j=7x
m-3.j=3x+20
as a pair of simultaneous equations ???
