How do you find the value of w if it is given that V=lwh?

I guess by V = l*w*h you mean volume =
length*width*height

To find w or the width, you need to
have the values for volume, height and length.

As V =
l*w*h, divide both the sides of the equation by
length*height

=> V/(l*h) =
(l*w*h)/(l*h)

=> V/(l*h) =
w

The width can be determined by dividing the
volume (V) by the product of length (l) and height (h).