7abc-3abc
25ab-(-3ab)
2a+3a
4xy-2xy
20xy/4xy
5bc+(-5bc)
8am-3am
7mn+3mn
(4cd)(10cdx)
6xyz+10xyz
5am
40c^2d^2 x
16xyz
10mn
5xy
0
28ab
4abc
2xy
5a
