Remember the equation of a line with slope m and y-intercept b:
[tex]y=mx+b[/tex]Which can be expressed in terms of functions by replacing y=f(x)
[tex]f(x)=mx+b[/tex]Any line with the same slope will be parallel to that equation.
By comparing with:
[tex]f(x)=-5x+6[/tex]We can know that its slope is equal to -5.
Since the "parallel slope" is just the slope, then