document.write( "Question 174364: The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 30 minutes of calls is $15.46 and the monthly cost for 84 minutes is $20.32. What is the monthly cost for 54 minutes of calls? \n" ); document.write( "
Algebra.Com's Answer #129310 by stanbon(75887)\"\" \"About 
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The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 30 minutes of calls is $15.46 and the monthly cost for 84 minutes is $20.32. What is the monthly cost for 54 minutes of calls?
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\n" ); document.write( "\n" ); document.write( "You have two points: (30,15.46) and (84,20.32)
\n" ); document.write( "slope = (20.32-15.46)/(84-30) = 4.86/54 = 0.09
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\n" ); document.write( "intercept ?
\n" ); document.write( "Form : y = mx + b; solve for \"b\":
\n" ); document.write( "15.46 = 0.09*30 + b
\n" ); document.write( "b = 12.76
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\n" ); document.write( "Equation:
\n" ); document.write( "cost = 0.09(minutes) + 12.76
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\n" ); document.write( "If minutes is 54 you get,
\n" ); document.write( "c(54) = 0.09*54 + 12.76
\n" ); document.write( "c(54) = $17.62
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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