26 000 8665 + 18 000 3426 =

To add the two numbers \( 26,000,8665 \) and \( 18,000,3426 \):

First, align the numbers by their decimal points:

   26,000,866.5
+ 18,000,342.6
----------------

Now, add them together:

   26,000,866.5
+ 18,000,342.6
----------------
   44,001,209.1

So, \( 26,000,866.5 + 18,000,342.6 = 44,001,209.1 \).