I am trying to find the x-intercept to a word problem with a linear equation of

Question

I am trying to find the x-intercept to a word problem with a linear equation of D(t) =533.5t + 6340.5. Where D is the debt in billions and t is the time in years. I know that to find the x-intercept I have to set y= 0. But when I enter that into the equation, 0 = 533.5t + 6340.5.........-6340.5=533.5t.......... which gives me -11.8847 on so on. but that does not make sense in the word problem I am trying to answer. How can the time in years be a negative number when the function is an increasing function and the line will never intersect the x axis? I am very confused on this so imediate help is greatly appreciated. 

Explanation / Answer

One way to look at this is: In your year zero (2000) the debtwas 6340.5. The question (the x intercept) is when was the debtzero at the current rate i.e. -11.8847 years meaning the year1988, about February 11. Of course, the debt startedwell before then but at a much smaller rate (the debt in 1978 wasabout 680 million) i.e. the rate of dept is accelerating.

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