Well, we're trying to figure out the rate at which the height of the balloon is changing. So if you call this distance right over here, this distance right over here, h, what we wanna figure out is dh dt. That's what we don't know. So what we'd wanna come up with is a relationship between dh dt, d theta dt, and maybe theta if we need it. Or another way to think about it, if we can come up with a relationship between h and theta, then we could take the derivative with respect to t, and we'll probably get a relationship between all of this stuff. So what's the relationship between theta and h? Well, it's a little bit of trigonometry.