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[ n+ (n+2) + (n+4) + .....(n+12) ] /7 = 16
[ (n+2) + (n+4) + .... (n+12) ] = 108
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well, multiply the first one by 7
[ n+ (n+2) + (n+4) + .....(n+12) ] = 16*7 = 112
[ (n+2) + (n+4) + .... (n+12) ] = 108
------------------------------------------------subtract
n = 112 - 108