How can I obtain toned arms and a flat stomach quickly?

So, I want to lose weight- so I’m 15 and I weigh around 71 Kgs and I’m 178 cm in height – so I’m not overweight. I am not very fat, but I’d like a tight stomach and toned arms because they’re flabby .

I’ve lost a lot of weight lately- but over a long period of time- now, I do around 40–50 sit ups for day for the stomach and just started doing the simple push ups- What exercises should I do to be able to obtain amazing results within a short-ish period of time.
Thank you for all your help ♥

~Oh yeah: I do watch what I eat btw- so please do not try and advise me about healthy eating :D