document.write( "Question 179491: i don't understand how to do this? can you please help? here is the problem:
\n" ); document.write( "a poster is 20 cm longer than it is wide. it is mounted on a piece of cardboard so that there is a 10 cm border on all sides. if the area of the border is 2400 cm squared what is the area of the poster? \n" ); document.write( "
Algebra.Com's Answer #134431 by nerdybill(7384)\"\" \"About 
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a poster is 20 cm longer than it is wide. it is mounted on a piece of cardboard so that there is a 10 cm border on all sides. if the area of the border is 2400 cm squared what is the area of the poster?
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\n" ); document.write( "Let x = width of poster
\n" ); document.write( "then
\n" ); document.write( "x+20 = length of poster
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\n" ); document.write( "Cardboard backing is:
\n" ); document.write( "x+10 = width
\n" ); document.write( "x+20 + 10 = length
\n" ); document.write( ".
\n" ); document.write( "\"border area\" = \"cardboard area\" - \"poster area\"
\n" ); document.write( "2400 = (x+10)(x+30) - x(x+20)
\n" ); document.write( "2400 = x^2+30x+10x+300 - x^2-20x
\n" ); document.write( "2400 = x^2+40x+300 - x^2-20x
\n" ); document.write( "2400 = 40x+300 -20x
\n" ); document.write( "2400 = 20x+300
\n" ); document.write( "2100 = 20x
\n" ); document.write( "105 cm = x (width)
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\n" ); document.write( "length:
\n" ); document.write( "x+20 = 105+20 = 125 cm
\n" ); document.write( ".
\n" ); document.write( "area = 105*125 = 13125 square cm
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