is just like this:



which is just like these:

 6 pencils          6 apples       $6
+6 pencils         +6 apples      +$6
+7 pencils         +7 apples      +$7 
----------         ---------      ---
19 pencils         19 apples      $19

which is just like this:

 6 square roots of five
+6 square roots of five
+7 square roots of five
-----------------------
19 square roots of five

which is exactly the same as:

 

Edwin