document.write( "Question 596951: I need help i am a parent trying to help my son with his homework his teacher gave them the answers to the problems and he has to show work i just do not know how to show the work if you could please help me it is algebra solving systems of equations by substituting -4x+y=6 -5x-y+21 X=-3 Y=-6 please help thanks \n" ); document.write( "
Algebra.Com's Answer #378021 by ankor@dixie-net.com(22740)\"\" \"About 
You can put this solution on YOUR website!
solving systems of equations by substituting
\n" ); document.write( "Assuming the problem is:
\n" ); document.write( "-4x + y = 6
\n" ); document.write( "-5x - y = 21
\n" ); document.write( ":
\n" ); document.write( "Arrange the 1st equation so we can use it for substitution
\n" ); document.write( "-4x + y = 6
\n" ); document.write( "Add 4x to both sides
\n" ); document.write( "y = 4x + 6
\n" ); document.write( ":
\n" ); document.write( "Now we can substitute (4x+6) for y in the 2nd equation
\n" ); document.write( "-5x - y = 21
\n" ); document.write( "-5x -(4x+6) = 21
\n" ); document.write( "-5x - 4x - 6 = 21
\n" ); document.write( "-9x = 21 + 6
\n" ); document.write( "-9x = 27
\n" ); document.write( "divide both sides by -9
\n" ); document.write( "x = -3
\n" ); document.write( ":
\n" ); document.write( "Find y using the equation y = 4x + 6, replace x wtih -3
\n" ); document.write( "y = 4(-3) + 6
\n" ); document.write( "y = -12 + 6
\n" ); document.write( "y = -6
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Check your solutions in the 2nd equation
\n" ); document.write( "-5(-3) - (-6) = 21
\n" ); document.write( "15 + 6 = 21; minus a minus is a plus \n" ); document.write( "
\n" );