.
In[1]:= solve = NSolve[{x - y == 1, 2 x + y == 1}, {x, y}]
Out[1]= {{x -> 0.666667, y -> -0.333333}}
In[2]:= Extract[solve, {1}]
Out[2]= {x -> 0.666667, y -> -0.333333}
In[3]:= Extract[solve, {2}]
During evaluation of In[3]:= Extract::partw: Part 2 of {{x->0.666667,y->-0.333333}} does not exist. >>
Out[3]= Extract[{{x -> 0.666667, y -> -0.333333}}, {2}]
In[4]:= x + y /. First[solve]
Out[4]= 0.333333
