The key technique in taking negation of a statement is to faithfully change every existential quantifier to universal quantifier, and vice versa and finally take the negation of the things inside the quantifiers. Remember this only works for the statements that have quantifiers all in the front of the statements.
In section D, I explained the truth table for p\to q. Notice that in mathematics, if p is false, then p\to q is always true no matter what q is.