code is here:

ENTITY top IS END top;

ARCHITECTURE example OF top IS
 SIGNAL w,x,y,z : integer := 0;
   BEGIN
   p1 : PROCESS(z)
    VARIABLE a : integer := 0;
   BEGIN
      a := a + 20;
    w <= w + 10;
  x <= a + w AFTER 10 ns;
  y <= a - w AFTER 20 ns;
  END PROCESS;

 p2: PROCESS
 BEGIN
 z <= (x + y) AFTER 30 ns;
 [![enter image description here][1]][1]
 WAIT ON x,y;
END PROCESS;
 END example;