What number makes the equation true?

31 - - 12=6

13

Step-by-step explanation:

The blank space is unknown so we can put in a variable

31 - x - 12 = 6

Then we should try to make it so the variable is on one side and all the numbers on the other

31 - x - 12 = 6

+12 + 12

31 - x = 18

-31 - 31

-x = - 13

*-1 * -1

x = 13

So your answer would be 13

31-13-12 = 6