Basically, every linear function can be expressed as:
[tex]y=ax + b[/tex], where [tex]a[/tex] is the slope.
So, the slope is 9 in your case.
To find y-intercept of the line you have to set [tex]x=0[/tex] because line intercepts y-axis when [tex]x[/tex] is equal to zero:
[tex]y=9*(0) - 3[/tex]
From here we can say that [tex]b[/tex] is the y-interception.
So, y-interception is -3 in your case.
