If it is 10 to 99 pages, use the number [(99-10)/1+1] * 2 =180.

For pages 100 to 199, use [(199-100)/1+1] * 3 = 300 digits.

9+ 180+300=489, which is beyond the range of 306.

So the number of pages must be in the range of 100 to 199.

(306-9-180)/3+9+90 =138 (page)