Just to add to what's been written above:
A number is only said to be expressed in 'standard index form' (a x 10^b) when a is between 1 and 10. (a can be exactly equal to 1, but not to 10).
So, if you simply write the answer to your multiplication as 11.25 x 10^-1 you have failed to produce an answer in standard index form.
So it's necessary to write 11.25 in standard index form itself, and then to multiply it by 10^-1:
11.25 x 10^-1 = 1.125 x 10^1 x 10^-1 = 1.125 x 10^0
Simply keep it in mind that the first term must be between 1 and 10, then you won't go wrong ;-)
Chris