solve the formula for the specified value
v=1/3 bh
solve for b

Answer:
The choice a.
[tex]B = \frac{3v}{h} [/tex]
Step-by-step explanation:
[tex]v = \frac{1}{3} Bh \\ \\ v = \frac{Bh}{3} \\ \\ Bh = 3v \\ \\B = \frac{3v}{h} [/tex]
I hope I helped you^_^