the problem is 2.56 x 1,000,000,000

Multiplying a number by  10  moves the decimal point to the right one place.

For example...      2 * 10  =  20     and     0.7 * 10  =  7

When we multiply  2.56  by  1,000,000,000 , we are multiplying  2.56  by  10 , 9 times.

So we need to move the decimal point to the right  9  places.

2.56 * 1,000,000,000  =  2,560,000,000.0

The decimal point goes at the very end of  2,560,000,000 , but it isn't necessary to write it since only zeros follow it.