Part b: do the number of books and the cost have a proportional relationship? explain.

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.

the answer is d

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you should talk someone who owns the website about it. you did not deserve to have all that hard work and time taken away. id watch videos of little puppies to cool you down, and maybe some nacho cheese doritos.