52 ___ 81
1 + 3 = ____
8 + 6 = ___
3 + 9 = ___
7 + 7 = ___
8 + ___ = 16
16 − 8 = ___
4 − 2 = ___
2 + 4 = ___
___ − 2 = 4
4 + ___ = 9
9 − ___ = 4
81 + 8 = ___
70 − 30 = ___