3 quintillion
3000000000000000000
The sum of 3,000,000,000,000,000,000 and 678,789,278,973,927 is 3,000,678,789,278,973,927. This is obtained by adding the numbers in the corresponding place values: starting from the right, adding the ones, tens, hundreds, thousands, etc. until the quadrillion place. The result is a very large number due to the significant digits in both addends.