<PRE><B>Question 1159602</B>
You should say what kind of method you need to use.


{{{system(A+B=10,C=4D,A+C=3,B+D=9)}}}


{{{system(A+B=10,A+4D=3,B+D=9)}}}, {{{A=10-B}}};


{{{system(10-B+4D=3,B+D=9)}}}


{{{system(-B+4D=-7,B+D=9)}}}


{{{system(B-4D=7,B+D=9)}}}-----------this much by just a couple of substitutions.  You can solve this for B and D, right?  You can then finish on your own for A and C?</PRE>