In a set of integers, one-half of the numbers are multiples of 7 and one-third of the numbers are multiples of 3. If one-fifth of the numbers are multiples of both 3 and 7, then what percentage of the number are multiples of 7 but not multiples of 21?
A) 9
B) 15
C) 30
D) 33.3
E) 60
A) 9
B) 15
C) 30
D) 33.3
E) 60