Find the sum of the digits of 777,777,777,777^2 - 222,222,222,223^2.

Find the sum of the digits of
$777,777,777,777^2 - 222,222,222,223^2$.

Formula: $a^2-b^2 = (a-b)*(a+b)$

$\begin{array}{|rcll|} \hline && \mathbf{ 777,777,777,777^2 - 222,222,222,223^2 } \\ &=& (777,777,777,777 - 222,222,222,223)*(777,777,777,777 + 222,222,222,223) \\ &=& 555,555,555,554*1,000,000,000,000\\ &=& \mathbf{555,555,555,554,000,000,000,000 }\\ \hline \end{array}$