Answer:
Missing number = 68
Explanation:
You can simply set up an equation like so:
.
Then, proceed to solve by isolating the x by itself.
x+(-56)=12
+56 +56 <--- Do the opposite operation on both sides to cancel the 56.
x=68
A quick pointer: A number plus a negative number is just subtracting so you can just work backwards.
Answer: 68.