v = 1/3Bh
Divide both sides by h.
v/h = 1/3B
Multiply both sides by 3.
3v/h = B
[tex] \boxed {B = \frac{3v}{h} } [/tex]
[tex]\dfrac{1}{3}Bh=v\ \ \ \ |\cdot3\\\\Bh=3v\ \ \ \ |:h\neq0\\\\\boxed{B=\dfrac{3v}{h}}[/tex]
