Problem uploading to board

Development Tools IDE 1.x
1

I am getting this error plz Someone help me

Arduino: 1.6.0 (Windows 7), Board: "Arduino Uno"

Sketch uses 1,030 bytes (3%) of program storage space. Maximum is 32,256 bytes.

Global variables use 9 bytes (0%) of dynamic memory, leaving 2,039 bytes for local variables. Maximum is 2,048 bytes.

avrdude: ser_open(): can't open device "\.\COM21": The system cannot find the file specified.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

This report would have more information with
"Show verbose output during compilation"
enabled in File > Preferences.

2

From tools -> ports, select the COM port associated with your Arduino

If no ports are listed, exit IDE, unplug+replug usb, restart IDE. If still not listed, you probably have a driver problem.