The algorithm of scientific notation? For example, how to multiply the - 10th power of 1.63 * 10 by the - 9th power of 2.55 * 10?

The algorithm of scientific notation? For example, how to multiply the - 10th power of 1.63 * 10 by the - 9th power of 2.55 * 10?

1.63*2.55=4.1565
-10+(-9)=-19
So it's 4.1565 to the - 19th power