Go to the gold mine and hit collect over and over. Eventually, you will get as much gold as your gold mine can store each time you press collect.
Getting a free P.E.K.K.A.:
Go to the labatory. Click info, x out, and try again until it glows red. When it does, click on it and a level 3 P.E.K.K.A. Comes out. Make sure you have room, or the hack won't work.