What should replace the ? mark in below figure.

Concept: Each row shows one number written twice, followed by a third value produced by a fixed two-step rule: square the repeated number, then add up the digits of that square. Before trusting the rule on the missing cell, it must reproduce every OTHER row's given third value exactly.

Application:

1. Row 1: 232 = 529; digit sum = 5 + 2 + 9 = 16, which matches the given third value (16).

2. Row 2: 292 = 841; digit sum = 8 + 4 + 1 = 13, which matches the given third value (13).

3. Row 3: 312 = 961; digit sum = 9 + 6 + 1 = 16 — this is the missing value.

Cross-check: The rule was confirmed independently on two different numbers (23 and 29) before being applied to 31, so it is not a fit to a single case. 16 repeating in row 1 and row 3 is only a coincidence of digit sums, not a separate pattern to worry about.