Prove or give a counterexample every sub graph of a

Question

Question: 1. Write the contrapositive of if x² > 100, then y has a sister.

2. Prove or give a counterexample: Every sub graph of a non-planar graph is non-planar.

3. Let C = {d,e,{d,e}, f }. List the elements in each of the following sets (or write 0 if appropriate). Be careful with your notation.

(a) C\{d, e}

(b) C\{{d, e}}.