I decrease a number by 26%, the answer is 9 x10^-7, what was the original number?

The number has been decreased by 26%, this means that the original number is 100-26=74% of the original value. 

Therefore 9 x 10^-7 = 0.74 x N, where N is the original number.

Hence N=(9 x 10^-7)/0.74 = 1.216 x 10^-6.