How can i state whether each graphs represents a function? ​

Which table shows a proportional relationship between miles traveled and gas used?

Which best describes the function on the graph? direct variation; k = −2 direct variation; k = -1/2 inverse variation; k = −2 inverse variation; k = -1/2

If the tip varies directly with the number of guest which equation represents between the tip, t, and the number of guest, g?