ANSWER
[tex] \boxed { r = \frac{Q}{8 {s}^{2} } }[/tex]
EXPLANATION
The given equation is;
[tex]Q=8rs^2[/tex]
We want to solve this equation for r.
This means that we need to isolate r, so that it will be on one side of the equation, while all other variables and constants are also on the other side.
Let us divide both sides of the equation by
[tex]8 {s}^{2} [/tex]
to obtain,
[tex] \frac{Q}{8 {s}^{2} } = \frac{8rs^2}{8 {s}^{2} } [/tex]
We cancel out the common factors to obtain,
[tex] \frac{Q}{8 {s}^{2} } =r[/tex]
Or
[tex] r = \frac{Q}{8 {s}^{2} } [/tex]
