Question 1056877
Let {{{ L }}} = the length in cm of the original sheet of brass
Let {{{ W }}} = the width in cm of the original sheet of brass
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After the squares are cut out from the corners, 
The new length = {{{ L - 2*3 }}} cm
The new width = {{{ W - 2*3 }}} cm
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The volume, after the sides are turned up to make a box, is
{{{ V = ( L - 6 )*( W - 6 )*3 }}} ( note the height will be {{{ 3 }}} cm )
given:
{{{ L = 2W }}}
{{{ V = 1248 }}} cm^3
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{{{ 1248 = ( 2W - 6 )*( W - 6 )*3 }}}
{{{ 1248 = ( 2W^2 - 6W - 12W + 36 )*3 }}} 
{{{ 2w^2 - 18W + 36 = 416 }}}
{{{ 2W^2 - 18W - 380 = 0 }}}
{{{ W^2 - 9W - 190 = 0 }}}
{{{ ( W - 19 )*( W + 10 ) }}}  ( just by looking at it )
{{{ W = 19 }}} cm  ( Can't use the negative value )
and
{{{ L = 2W }}}
{{{ L = 38 }}} cm
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The dimensions of the original sheet of brass are 19 x 38 
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check answer:
{{{ V = ( L - 6 )*( W - 6 )*3 }}} 
{{{ V = ( 38 - 6 )*( 19 - 6 )*3 }}} 
{{{ V = 32*13*3 }}}
{{{ V = 1248 }}} cm3
OK