X intercepts: (9,0)
y intercepts: (0,-6)
B + 7.4 = 4.8
b = 4.8 - 7.5
b = -2.7
hope this helps :)
You'd want to use a vertical line test.
1st image: Every vertical line cuts the graph at at most one point
2nd image: The vertical line x = 1 cuts the graph at more than one point
3rd image: The vertical line x = 1 cuts the graph at 2 points
4th image: The vertical line x = -2 cuts the graph at 2 points
Hence, graph 1 (1st image) is a function.