Calls from a call box are charged per minute at one rate for the five minutes, then a different rate for each additional minute. if a 7-minute call costs $4.25 and a 12-minute call costs $5.50, find each rate.
a.$ 1.50 per minute at one rate for the first 5 minutes and $0.50 per minute thereafter
b.$3.20 per minute at one rate for the first 5 minutes and $0.55 per minute thereafter
c.$0.75 per minute at one rate for the first 5 minutes and $0.25 per minute thereafter
d.$2.40 per minute at one rate for the first 5 minutes and $0.75 per minute thereafter
which answer is it

  c.  $0.75 per minute at one rate for the first 5 minutes and $0.25 per minute thereafter

Step-by-step explanation:

The last 5 minutes of the 12-minute call cost ...

  $5.50 -4.25 = $1.25

so the per-minute rate at that time is ...

  $1.25/(5 min) = $0.25/min . . . . . . . . matches choice C only

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You know the answer at this point, but if you want to check the rate for the first 5 minutes, you can subtract 2 minutes from the 7-minute call to find that ...

  The first 5 minutes cost $4.25 - 2·0.25 = $3.75, so are charged at ...

     $3.75/(5 min) = $0.75/min . . . . . . . matches choice C

your answer would be 10x - 1