100 is equal to [tex]10^{2} [/tex], So, when you multiply the scientific notation by 100, you should add 2 to the exponent of 10 in that scientific notation:
For example;
[tex]9.12* 10^{8} * 100[/tex]
= [tex]9.12* 10^{8} * 10^{2} [/tex]
= [tex]9.12* 10^{8+2}[/tex]
= [tex]9.12* 10^{10}[/tex]
