The density is the amount of mass per unit of volume of any material. You can find the density by using the formula:
[tex]d=\frac{m}{v}[/tex]
where d is the density, m is the mass and v is the volume
you have the mass and the volume so you just have to replace the variables in the formula with the values they are giving you, like this:
[tex]d = \frac{m}{v} = \frac{114g}{8 {m}^{3} } = 14.25 \frac{g}{ {m}^{3} }[/tex]
The density of wooden plank is 14.25g/m^3
