First, we need to find the slope of line a, using the next formula
![m=(y_2-y_1)/(x_2-x_1)](https://img.qammunity.org/2023/formulas/mathematics/high-school/78uaqhwt0aws3qfwxigaftpihnmb1gzxtp.png)
where
(1,-4)=(x1,y1)
(9,-6)=(x2,y2)
we substitute the values
![m=(-6+4)/(9-1)=(-2)/(8)=-(1)/(4)](https://img.qammunity.org/2023/formulas/mathematics/college/q5gxp6errwxh3rhkwrclc6b87jb3lqbg14.png)
The slope of a perpendicular line to line a is the inverse of the slope we found therefore the slope of line b will be
![m_b=4](https://img.qammunity.org/2023/formulas/mathematics/college/6hcz2bhdwivw0r02olbu58ehgip4q0xxx7.png)
then we will use the slope-point form to find the equation of line b
![y-y_1=m(x-x_1)](https://img.qammunity.org/2023/formulas/mathematics/high-school/csobd57zth7rh9k4hz9amldzpq2owf0z4j.png)
where
(-6,-24)=(x1,y1)
![y+24=4(x+6)](https://img.qammunity.org/2023/formulas/mathematics/college/xk2gsxsl3k0end92g5r0u3zfprjlha3irv.png)
then in order to find the equation in the slope-intercept form, we need to isolate the y
![\begin{gathered} y+24=4x+24 \\ \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/kgdigokcg60sy85i3p5zxysyru3gqpzpon.png)
![y=4x+24-24](https://img.qammunity.org/2023/formulas/mathematics/college/7b6t3xlh5bdxohtxj32maopra9285s44pt.png)
![y=4x](https://img.qammunity.org/2023/formulas/mathematics/high-school/6yhq5l9ez0rs3whhqxkdo7mhfdidpcy3mr.png)
The equation of line b is y=4x