What is the equation of the line in slope intercept form form

Those points you can see on the graph.
The first one refers to the x value and the second, to y value. If you notice, when you have x = 0, y = 3. When x = -5, y = 0.

When the line intercepts one of the axis, means the other coordinate is = 0.
3 is y intercept, it means the x value of that point is 0. The same happens to the x intercept - 5. It means the y value of that point is 0.

A ( -5 | 0 )
B ( 0 | 3 )

m = Delta y / Delta x.
Delta y is the variation over the x-axis. Delta x, the x axis.

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