document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=698784>Question 698784</A>: <I><SPAN STYLE=\"word-break: break-all;\"> solve by using subsitution<BR>\n" );
document.write( "4x+4y=-20<BR>\n" );
document.write( "x-4y=15<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #431050 by </B><A HREF=/tutors/aboutme.mpl?userid=Simnepi><B>Simnepi(216)</B></A><img src=\"/images/stars/stars-09.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Simnepi><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=Simnepi><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=431050\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> 4x+4y=-20     Equation (1)<BR>\n" );
document.write( "x-4y=15       Equation (2)<BR>\n" );
document.write( "Rearranging (2) gives<BR>\n" );
document.write( "x=15+4y     Equation (3)<BR>\n" );
document.write( "We can now substitute the value of x from (3) into (1)<BR>\n" );
document.write( "4*(15+4y)+4y = -20<BR>\n" );
document.write( "Multiplying out and simplifying we get<BR>\n" );
document.write( "60+20y = -20<BR>\n" );
document.write( "therefore 20y = -80<BR>\n" );
document.write( "which gives y = -4<BR>\n" );
document.write( "Now we can substitute this value of y into either (1), (2) or (3) to find the value of x<BR>\n" );
document.write( "lets use (3)<BR>\n" );
document.write( "x=15+4y<BR>\n" );
document.write( "x=15+4*-4<BR>\n" );
document.write( "so x= -1 </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );