SOLUTION: A car wash charges a flat rate for the first 8 minutes of washing time and also charges a certain amount for each additional minute of washing time. Gina took 12 minutes to wash h

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Question 174669This question is from textbook Algebra 2, Texas Edition
: A car wash charges a flat rate for the first 8 minutes of washing time and also charges a certain amount for each additional minute of washing time. Gina took 12 minutes to wash her car and it cost her a total of $5.00. Kris took 17 minutes to wash his truck at a total cost of $6.25. Write an equation that models the total cost ot a car wash as a function of the number of minutes spent washing a vehicle. With this information, using the equation, what is the slope of a line parallel to the line in the first part making by the equation into form. This question is from textbook Algebra 2, Texas Edition

Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
Let the flat rate for the 1st 8 min =
Let the cost/min after the 8 min =
Let = the time in minutes after 8 min that it takes to wash car
Let = the toal cost to wash car

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For Gina:

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For Kris:

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Now put the data from each case into the geral equation:
(1)
(2)
There are 2 equations and 2 unknowns, so it's solvable
Subtract (1) from (2)

Now find
(1)

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Now I can rewrite the general equation as:

Here's a plot:

The slope is