this step can explain you, how to connecting APT trough network with proxy. folow this step :
1. create 'proxy' file
$sudo touch /etc/apt/apt.conf.d/proxy
2. edit 'proxy' file
$sudo touch /etc/apt/apt.conf.d/proxy
3. add this script
Acquire::http::Proxy "http://proxy_ip:proxy_port";
4. save and now you can update or install from APT with proxy,,
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