How to connect through a proxy on windows

[Nina0109]

Hi @cj, I'm using sftp in sublime3, trying to connect my server B which can only access though a proxy A.
I can connect to A with a key file, by doing like this: "ssh_key_file": "D:/sshkeys/sublime_keys_jnyang.ppk".
Now how can I connect to B?
I tried he following, but failed.
"host": <ip_of_B>,
"user": <user_on_B>,
"password": <passwd_of_B>,
"port": <port_of_B>,
"sftp_flags": [
"-o", "ProxyCommand=ssh -p user@ip_of_A -i /path/to/A's key -W %h:%p"],
The rror message is "failure (Connection timeout)", can you tell me what's wrong? Thanks.