(1)It's all good! 没事！一切都好！

Sorry I forgot to call you back! 对不起！我忘了回电了！It's all good! 没事！

(2)no sweat 没事

Thanks for helping me move yesterday! 谢谢你昨天帮我搬家咯！ No sweat! 没事！

(3)piece of cake 小事一桩，很容易

Thanks for helping me throw that party. It was a huge success! 谢谢你帮我开这个party! 太成功了！ It was a piece of cake! 小事一桩。