How to make a picture with 200×280 pixels less than 30K in JPG, GIF and PNG formats?

Using photoshop should be easy. Open the picture with photoshop, select the image size, directly input the corresponding size unit to be changed and select pixels. If the aspect ratio is consistent with the original image, select the constraint ratio, then select the saving format, select the desired format, and then select the saving quality.

Just do it.