Question 988915
They are giving you a slope for the graph 
of {{{ t = f( c ) }}} 
slope = [ change in t ] / [ change in c ] for the points:
( 0, 6000 ) and ( 12000, 8000 )
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Use the general point-slope formula:
{{{ ( t - 6000 ) / ( c - 0 ) = ( 8000 - 6000 ) / ( 12000 - 0 ) }}}
{{{ ( t - 6000 ) / c = 2000 / 12000  }}}
{{{ ( t - 6000 ) / c = 1/6 }}}
{{{ t - 6000 = ( 1/6)*c }}}
{{{ t = ( 1/6 )*c + 6000 }}}
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If they make only trucks, then {{{ c=0 }}} and
{{{ t = 6000 }}}
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check:
Does it go through the point ( 12000, 8000 )?
{{{ t = ( 1/6 )*c + 6000 }}}
{{{ 8000 = (1/6)*12000 + 6000 }}}
{{{ 8000 = 2000 + 6000 }}}
{{{ 8000 = 8000 }}}
OK