The formula for the density of a bacteria population is \dfrac NA A
N

start fraction, N, divided by, A, end fraction where there's an average of NNN bacteria in an area size AAA.
Guang and Orion are doing an experiment in school for which they need to measure the density of a bacteria population after a certain solution has been introduced. Guang reports a density of 450045004500 bacteria per square centimeter and Orion reports a density of 505050 bacteria per square millimeter.