Question 1208092
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        The solution in the post by @mananth is incomplete.


        The complete solution should be,  OBVIOUSLY,  a piecewise linear function   C(x)

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;with one formula for &nbsp;0 <= x <= 1000 &nbsp;kilowatts-hours and another formula for &nbsp;x > 1000 kilowatt-hours.



<pre>
For 0 <= x <= 1000 kWh, the formula is

    C(x) = 4.50 + 0.042345x  dollars  (rounded to the closest cent).


At x = 1000 kWh, it gives  C(1000) = 4.50 + 0.042345*1000 = 46.845 dollars before rounding,

                                                       or = 46.85 dollars after rounding.


For x > 1000 kWh, the formula is

    C(x) = 46.85 + 0.053622*(x-1000)  dollars  (rounded to the closest cent).


It is a complete solution to the problem.
</pre>

Solved in full, &nbsp;with complete explanations.



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When you ask where the coefficients come from, this is a completely childish 
question - it does not correspond to the level of the problem.


The level of the problem is about 9-th grade.


The level of the question "where the coefficients come from" is about 3-rd or 4-th grade.


So, you try to solve a problem of the 9-th grade without having solid base/knowledge of the 4-th grade.


It is what I see from your post.