Answer: See attached or top left no, top right yes, graph 5 yes, and graph 6 no.
Explanation:
When graphed, functions need to pass the vertical line test to be a function. This is a test in which you pass an imaginary (or real) vertical line across the graph. If there are ever two points of the graph touching this line at once, it's not a function. See attached, I have run this test through all the functions to determine which are and aren't functions.