Given, P=185220,R=5% (increases) and n=3yr.

According to the formula,

Population n yr ago = \( \Large  \frac{P}{ \left(1+\frac{R}{100}\right)^{n}} \)

\( \Large  \frac{185220}{ \left(1+\frac{5}{100}\right)^{3}}  = \)\(  \Large \frac{185220\times 20\times 20\times 20}{21\times 21\times 21} \)

=\( \Large 20\times 20\times 20\times 20 \)=160000