algebra addistion
posted by MARKO .
can you check my answers
13  9 i got 4
15  3 i got 12
12 + 3 i got : 15
31 + 12 i got: 43
+9 + (+7) i got: 16
21
18 + 21 i got : 39
5 +(13) i got: 7
18 + (3) i got: 21
2 + (+17) i got: 15
15 + (9) i got: 6
5 + 21 i got 26
10 + 3 i got: 7

all good except:
5 +(13) = 18
btw, what is that 21 stuck in there?
I ignored it