you can add them like this:
so if 156 + 213 + 109 was the equation then you would
first put them in order from biggest to smallest
213
156
+109
-----------
then add:
¹ ← ←
213 ↑
156 ↑
+109 ↑
---------↑ ( carry the 10 )
478 (add the ¹ )
then you get the answer 478!
hope that helps :)
