If k is the greatest positive integer such that 3^k is a divisor of 21! then k = Select the correct option:  A) 3  B) 4  C) 5  D) 6  E) 9
21/3= 
<gadget id="calculator">21/3</gadget>
<output>7</output>
7   21/9=2.33=2   7+2= 
<gadget id="calculator">7+2</gadget>
<output>9</output>
9   k=9   Answer: 9
<result>E</result>
If k is the greatest positive integer such that 3^k is a divisor of 21! then k =