2) division

3) multiplication

4) identity

5) addition

6) symmetry

7) substitution

8) subtraction

9) distributive

10) symmetry

11) X = 7 division

12) 3X=27 addition, X=9 division

13) X=18 multiplication

14) 7X+3X = 100 distributive, X=10 division

15) X=7 subtraction

16) X=35 addition

17) X/8=-2 subtraction, X=-16 multiplication

18) X = C / (A+B) division

19) X=X division (X can be anything)