The percentage of newsprint used which is made from recycled-content newsprint shall be calculated in tons used on an annual basis and shall increase to:

1. (a) Thirty percent on and after January 1, 1994.
2. (b) Thirty-five percent on and after January 1, 1996.
3. (c) Forty percent on and after January 1, 1998.
4. (d) Fifty percent on and after January 1, 2000.