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Math·Algebra·Linear functions

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A plumbing company charges its customers $112 for the first hour of a plumbing service call and $40 for each additional hour, plus the cost of plumbing parts. Which equation represents the total cost y in dollars, for an x-hour plumbing service call where the cost of parts was $z and $x\ge 1$?

A

$y=40x+z$

B

$y=40x+z+72$

C

$y=112x+z$

D

$y=112x+40z+72$