The average of 9 observations was 9, that of the 1st of 4 being 10 and that of the last 4 being 8. What was the 5th observation? Choose the most appropriate option:
A) 4
B) 5
C) 6
D) 7
E) 8
1 to 9 = 9 * 9= 
<gadget id="calculator">9 * 9</gadget>
<output>81</output>
81   1 to 4= 4 * 10= 
<gadget id="calculator">4 * 10</gadget>
<output>40</output>
40   4 to 9= 6 * 8= 
<gadget id="calculator">6 * 8</gadget>
<output>48</output>
48   5th= 48 + 40= 
<gadget id="calculator">48 + 40</gadget>
<output>88</output>
88 – 81= 7   ANSWER:7
<result>D</result>
The average of 9 observations was 9, that of the 1st of 4 being 10 and that of the last 4 being 8. What was the 5th observation?