crate is a 3d has a constant base area hence
[tex]volume = base \: area \times length \\ volume = 48 \\ base \: area \: = 16 \\ solving \: for \: length \\ \frac{volume}{base \: area} = length \\substituting \: the \: values \: \\ \frac{48}{16} = 3 \: so \: the \: length \: is \: 3 \: feet[/tex]