49 seemed like the intuitively obvious solution - but, when I started searching for a concrete rule to justify that answer (connecting 27, 38 and 49 to the numbers above them in each column), I couldn't find one that worked for 49.
I did, however, find a rule that works for 27 and 38:
(3rd row * 2nd row) - 1st row = 4th row
This rule gives the following results for each column:
(7 * 4) - 1 = 27
(8 * 5) - 2 = 38
(9 * 6) - 3 = 51
So now, I maintain that the answer is 51

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