The product of the slopes of this line and the line perpendicular to it is equal to -1.
Note that the slope if the coefficient of x.
Let
[tex] \alpha [/tex]
be the slope of the given line.
Let
[tex] \beta [/tex]
be the slope of the line perpendicular to it.
I can therefore say,
[tex] \alpha \times \beta = - 1[/tex]
[tex] \frac{ - 4}{3} \times \beta = - 1[/tex]
[tex] \beta = \frac{ - 1}{ \frac{ - 4}{3} } [/tex]
[tex] \beta = \frac{ - 3}{ - 4} = \frac{3}{ 4} [/tex]
The slope is 3/4