Any number multiplied by 1 equals itself, when the number 1 has zeros after it, just add the number of zeros to the end of the number being multiplied.
For example 9 x 1 = 9,
9 x 10 = 90 ( which is 9 x 1 and just add the one zero)
9 x 100 = 900 ( which is 9 x 1 , then add the two zeros)
So for your problem:
100000 x 89555
Multiply 89555 by 1, then add five zeros to the end:
100000 x 89555 = 8,955,500,000