To find the density of a piece of material, you need to measure its volume. The picture shows a piece of wood. It is 0.5 cm thick.
0.5 cm
Measure the picture and find the volume of the piece of wood.
Give your answer in cm3.

Explanation:

density =mass/volume

volume is equal to lengthXheightXwidth

if it is a cube then all three of them will same

3. dark matter

empty space could also be a simple vacuum

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m