title: Java code to solve dynamic equation with one unknown
body: <p>I my program there are various equations such as <code>x = y + z</code>.</p>
  
  <p>When the user has input all but one of the equation-variables, I want my program to
  calculate the unknown:</p>
  
  <p>User inputs <code>y=5 and z=2</code> --> <code>unknown x = 5 + 2 = 7</code></p>
  
  <p>User inputs <code>x=1 and y=3</code> --> <code>unknown z = 1 - 3 = -2</code></p>
  
  <p>I have many equations and want to avoid to manually have to isolate every variabel...hope u understand.</p>
  
  <p>I've tried both JEP and JScience, both without luck.</p>