Proving a Discrete math problem

[sportlover36]

Another one of my homework asks is this true or false and prove it:

For all sets A, B, and C if A U C is a subset of B U C then A is a subset of B

Please help!

 

[ideasrule]

Always try to come up with a counterexample. What happens if C is the set of all living things and A is the set of all humans?

 

[daveyinaz]

Consider
$$A = \{ 1 \}$$
$$B = \{ 3 \}$$
$$C = \{ 1, 2 \}$$