Answer:
[tex]\large\boxed{s=\sqrt{\dfrac{3V}{H}}}[/tex]
Step-by-step explanation:
[tex]\dfrac{1}{3}s^2H=V\qquad\text{multiply both sides by 3}\\\\3\!\!\!\!\diagup^1\cdot\dfrac{1}{3\!\!\!\!\diagup_1}s^2H=3V\qquad\text{divide both sides by}\ H\\\\s^2=\dfrac{3V}{H}\Rightarrow s=\sqrt{\dfrac{3V}{H}}[/tex]