The average of 10 result is 42. Average of the first 7 of them is 30 and that of the last 7 is 80. Find the 8th result?  Choose the correct choice from the following choices:
A) 35
B) 37
C) 70
D) 75
E) 50
Sum of all the 10 results = 10 * 42= 
<gadget id="calculator">10 * 42</gadget>
<output>420</output>
420   Sum of the first 7 of them= 7 * 30= 
<gadget id="calculator">7 * 30</gadget>
<output>210</output>
210   Sum of the last 7 of them= 7 * 80= 
<gadget id="calculator">7 * 80</gadget>
<output>560</output>
560   So, the 8th number= 420+ 210 - 560= 
<gadget id="calculator">420+ 210 - 560</gadget>
<output>70</output>
70.   70
<result>C</result>
The average of 10 result is 42. Average of the first 7 of them is 30 and that of the last 7 is 80. Find the 8th result?