The graph above shows the consumption of fossil fuels around the world and in the US since 1960. US consumption decreased from 1970 to 2009, while the world average consumption remained approximately even from 1970 to 2009. Why did US consumption decrease?
A) The US population dropped between 1970 and 2009
B) The US population became aware of the fossil fuel dependency and have reduced their consumption.
C) The US is running out of fossil fuels, and fossil fuels are too expensive to purchase from foreign sources.
D) None of the above.

They way i figured it, i got the answer of a. $120,200

Bis the answer to this question

You need to figure out at which x-value does the graph has a tangent line slope of -1.remember, the derivative is the slope of the tangent line. so find the derivative function and set it to equal -1 to find the x-value that will have a tangent line slope of 0.differentiate with the chain rule.    set the derivative to equal -1 and solve for x.      take log base 10 of both sides. also recall that  .    so the x-coord of the point of tangency is .the y-coordinate of this point of tangency can be calculated using the original function:     using point-slope form, the equation of the tangent line is      the x-intercept of this tangent line is when the graph is at y=0.    this rounds off to  .choice c.