Hey there! :)
B = 3 · v/h
To solve for v, we must isolate the variable. To start off, let's first multiply both sides by h.
B · h = 3 · v/h · h
Simplify.
Bh = 3 · v
Simplify.
Bh = 3v
Divide both sides by 3.
Bh ÷ 3 = 3v ÷ 3
Simplify.

Therefore, our red variable is :

~hope I helped!~