i dont know how u solv that but here is my approach
x x x x
y y y y
+ z z z z
---------------------------------
y x x x z
---------------------------------
so we can say that
z z from zero's place
x x+y+z; for ten's place so x from both LHS and RHS get cancel and we will get y -z;
same for hunderads and thousand place
for Ten Thousand place we get y x+y; i.e. x 0;
so we get x 0; y -z;
