



 
HI, I am going to number the equations
Notice that the first and second equation both have an $a$ and one has a $b$ and the other a $c.$ I want to use them to get one equation with only the variables $b$ and $c.$ If I take the left side of equation 2 and subtract the left side of equation 1 then I must get the right side of equation 2 minus the right side of equation 1. That is \[(a + c) (a + b) = 13  8\] which on simplification becomes \[c  b = 5.\] Equations three and four both have a $d$ and and one has a $b$ and the other a $c.$ can you do something similar to what I did with the first and second equations to obtain another equation with only the variables $b$ and $c?$ Once you have two equations in $b$ and $c$ use a similar technique to obtain an equation in only the variable $c$ solve it for $c$ and work backwards to find $a, b$ and $d.$ Penny 



Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 