Ok everyone, new to the forum here. I just started taking Calc 2 (online) after graduating 8 years ago. Taking it to apply for master's in physics, so I really need a good grasp here. So I'm a little rusty and it's hard to get help in an online class. Anyways, I've been doing well with understanding how to find volumes by revolution but then I got to this problem and I'm stumped. Is there anyone that can give me a detailed, step by step instruction on how to go about it? I found the answer online, but I'm not just trying to get a good grade, I really need to understand this. That would be awesome. Anyways, here's the problem.

(also, I know there are other ways to do it, but I've been asked to use the washer method, so I'd like to use that).

The disk x^{2}+y^{2}≤a^{2}is revolved about the line x=b (b>a) to generate a torus. Find its volume.

Thanks in advance.