$$\\P=500e^{kt}\\\\
800=500e^{k*1}\\\\
1.6=e^k\\\\
ln(1.6)=k\\\\
so\\\\
P=500e^{ln(1.6)*t}\\\\
when\;\; t=3\\\\
P=500e^{ln(1.6)*3}\\\\
P=500e^{3ln(1.6)}\\\\$$
$${\mathtt{500}}{\mathtt{\,\times\,}}{{\mathtt{e}}}^{\left({\mathtt{3}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{1.6}}\right)}\right)} = {\mathtt{2\,047.999\: \!999\: \!999\: \!999\: \!5}}$$
There will be 2048 insects. 