 So, the next one says the frequency of the nitrogen laser used in the LiDAR applications for measuring air pollution is 8.9 times 10 to the 14th hertz. What is the wavelength of light emitted by this laser? So again, you're probably going to be given the speed of light constant, so you don't have to memorize that. It tells you what the frequency is. So let's write that down first. The frequency is 8.9 times 10 to the 14th hertz. That's a 14. Recall that that's per second. So if you want to, you can think of this as 8.9 times 10 to the 14th divided by 1 second. And again, that's the way I like to think about it, especially when I'm teaching people where it's new to them. The other thing it tells us is that we're looking for the wavelength, OK? So we do know the equation we said it last time, c equals frequency times wavelength. So again, let's just isolate the variable that we're looking for, which is wavelength. It's going to be c divided by frequency. And again, I like to split this up, but we did that last time. So let's just skip that splitting up step and just remember what we did last time. OK, so notice the frequency is on the bottom here. So that's divided by, right? So you kind of want to flip that thing over like that. And that way, you can cancel out your seconds. So when it's divided by, you can do a multiply by the first. So everybody remember that mathematical rule. So when we do that, what do we do? Cancel out our seconds, and we get meters. So meters are good unit for length, right? Yeah, that's a pretty good unit for length. So let's just, so we know we're on the right track. Normally, a lot of times, you'll see these presented in nanometers, units of nanometers. So we can convert it to that if we want to in a second. So just 3 eb. So how many savings on this one? 2 again. So I got 3.4 times 10 to the negative 7 meters. So negative 7, that's kind of a real small way of reporting meters. Usually you want to report things in units that are appropriate to report them in. So it would be nice to think of this as some other more normal type of unit. So let's multiply it by 1 times 10 to the negative 9 meters or 1 nanometer. So 37 nanometers, but we got to take that to 2 sig figs. So we could say 340. So that would be 2 sig figs, right? Is everybody OK with that being 2 sig figs? There's no decimal place after the 0. Are there any questions on this one? Questions? Questions? Everybody cool? OK, we'll kill you.