In the reading room of a library, there are 23 reading spots. Each reading spot
consists of a round table with 9 chairs placed around it. There are some readers such
that in each occupied reading spot there are different numbers of readers. If in all there
are 36 readers, how many reading spots do not have even a single reader?  Choose one.
A) 12 B) 13 C) 14 D) 15 E) 16
1+2+3+4+5+6+7+8= 
<gadget id="calculator">1+2+3+4+5+6+7+8</gadget>
<output>36</output>
36   so, 8 spots are occupied by users    23-8= 
<gadget id="calculator"> 23-8</gadget>
<output>15</output>
15   ANSWER:15
<result>D</result>
In the reading room of a library, there are 23 reading spots. Each reading spot
consists of a round table with 9 chairs placed around it. There are some readers such
that in each occupied reading spot there are different numbers of readers. If in all there
are 36 readers, how many reading spots do not have even a single reader?