 So let's do this one now. It says determine the energy of a mole of photons with the frequency of 3.9 times 10 to the 13th hertz. Okay, so there's a few things in there that hopefully you've caught on to. So they're thinking, or they want you to do a mole of photons. So for this equation, of course, you're going to have to remember the energy equation equals NH frequency. Okay, so when you're given frequency, it's best to use this equation instead of converting it to wavelength using the Rieberg energy equation, which seems a little backwards, obviously. You also have to know that you're going to use Planck's constant, but that's going to give it to you, right? So 6.626, very square kilogram. Yeah, it's on that revision that I gave you before. So we're looking for the energy associated with a mole. So the other thing is a mole, right, is the number of photons. It's going to be 6.022 times 10 to the 23rd photons. If somebody wants to get that door, they'll be lost. So I don't have to do it for them. You wouldn't see the game. I know you need very much more, but so just plug it in and then you should get what you want. So N in this case, it's not one photon. It's a mole of photons, right? So 6.022 times 10 to the 23rd. And if you want to think about it, it's photons per mole. In fact, let's write that out. You can see all the units. Times Planck's constant, 6.626 times 10 to the negative 34 meters squared kilogram per second. Hertz, remember, that's another way of saying first again. For the constant, don't you have to have time seconds again? Or was it? No, that's a different problem. And again, if you thought that, why don't you cancel out your unit to figure it out, okay? So do that first. Okay, so 3.9 times 10 to 13. Are you going to cancel any of those units out? No, but hopefully you remember that 1 meter squared kilogram per second squared equals 1 joule. That's cool with that.