8.75878476e19
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Another contributor increased the precision of the answer:
The sum is the same number given in the question,
with the last two digits being 86 instead of 78 .
the answer is 56
8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 + 8 = 72
56
Another way to write that is 8x8. The answer is 64.
40
32
32
The total sum is 56
(-8) + (-8) + (+2) = -8 - 8 + 2 = -14
120
89
8 + 8 + 6 + 3 + 4 + 3 = 32