I think it would be 2 because it looks like 6 is the total and 3 is a side number so if you were to multiply 3 times 2 it would be 6. I hope this is correct!
One less limb than yesterday! so let’s assume like a regular human the mutant has 4 limbs. he grows another 5 and now he’s got 9 limbs. he loses 12 so 9-12 equals -3, plus 2 is -1.