Determine the sum of the digits of

Question

1) 777 777 777 777^2 - 222 222 222 223^2

Answer 1

Factorize the difference of two squares:
777 777 777 777^2 - 222 222 222 223^2
=(777777777777+222222222223)*(777777777777-222222222223)
=1000000000000*555555555554
=555555555554000000000000

The sum of the digits
= 12*5-1
=59