document.write( "Question 403333: Suppose that the credit remaining on a phone card( in dollars) is a linear function of the total calling time( in minutes). When graphed, the function gives a line with a slope of -0.13. There is $22.60 in credit remaining on the card after 20 minutes of calls. How much credit was there after 8 minutes of calls? \n" ); document.write( "

Algebra.Com's Answer #285225 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"C\"$ = credit remaining on card
\n" ); document.write( "given:
\n" ); document.write( " $\"C%28t%29+=+-.13t+%2B+b\"$
\n" ); document.write( " $\"22.6+=+-.13%2A20+%2B+b+\"$
\n" ); document.write( " $\"22.6+=+-2.6+%2B++b\"$
\n" ); document.write( " $\"b+=+25.2\"$
\n" ); document.write( "the equation is $\"C%28t%29+=+-.13t+%2B+25.2\"$
\n" ); document.write( " $\"C%288%29+=+-.13%2A8+%2B+25.2\"$
\n" ); document.write( " $\"C%288%29+=+-1.04+%2B+25.2\"$
\n" ); document.write( " $\"C%288%29+=+24.16\"$
\n" ); document.write( "There was $24.16 worth of credit left
\n" ); document.write( "Here's a plot:
\n" ); document.write( " $\"+graph%28+400%2C+400%2C+-10%2C+25%2C+-10%2C+34%2C+-.13x+%2B+25.2%29+\"$ \n" ); document.write( "

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