we have
[tex]F=\frac{1}{7}\cdot\pi\cdot r^2x[/tex]solve for x
step 1
Multiply by 7 both sides
[tex]7F=\pi\cdot r^2x[/tex]step 2
Divide by (pi*r^2) both sides
[tex]\begin{gathered} \frac{7F}{\pi r^2}=x \\ x=\frac{7F}{\pi r^2} \\ \end{gathered}[/tex]