We denote triangle ABC, angle A measures 90°, angle B measures 30° and angle C measures 60°.
We apply the cosine of 30 degrees, becuase m(∡A) = 90° and find the hypotenuse of triangle ABC:
cos = (adjacent side) / (hypotenuse)
⇔ cos B = AB/BC ⇔
⇔ cos 30° = 8√3/v ⇔
⇔ √3/2 = 8√3/v ⇔
⇔ √3 • v = 2 • 8√3 ⇔
⇔ v√3 = 16√3 ⇔
⇔ v = 16√3 ÷ √3 ⇔
⇔ v = 16 millimeters
Hope that helps! Good luck! :)