Insert the missing character depicted by ‘?’

In each cross, the centre number equals the sum of the four end numbers minus 2: 0 + 6 + 2 + 4 = 12 → 10, and 6 + 2 + 8 + 10 = 26 → 24. For the third, 4 + 14 + 10 + 12 = 40, so the centre is 38.