The minimum number of families in each month for which at least one adult or minor child head of household must be engaged in work as defined in paragraph (2) of this subdivision must be as follows:

(i) for Federal fiscal year 1997: 25 percent of the number of cases;

(ii) for Federal fiscal year 1998: 30 percent of the number of cases;

(iii) for Federal fiscal year 1999: 35 percent of the number of cases;

(iv) for Federal fiscal year 2000: 40 percent of the number of cases;

(vi) for Federal fiscal year 2002 and thereafter: 50 percent of the cases.