If the number of subscribers increases by 75% each year, then the number of subscribers each year is 175% the number of the previous year. So we need to multiply by 1.75 each year to get the next years number.
Since 2008 is 23 years after 1985, we'd have to multiply the 1985 number by 1.75 twenty-three times:
285 (1.75)^23 ≈ 110,845,988
That seems a bit crazy, since Glenwood is a small town, but so is a 75% growth each year for 23 years.