 This one says iron solidifies in a body-centered cubic structure The side of the cubic cell for iron is 287 picometers. What's the radius of an iron at? So if you recall, right? body-centered cubic has the formula of 4r equals s square root of 30. This is for the body center Not for the body center. That's for the face center. Yeah Okay, so sorry where was I? It says that the side of the cubic cell for this is 287 So we're looking in this case for the radius of the iron atom and all we have to do is rearrange this of course s square root of 30 divided by 4 equals the radius So now just plug each other again at once it and picometers so and How many six things three so 124 That's a reasonable number if you're getting somewhere about Reasonable numbers Are there any questions on this one pretty straightforward again if you memorize the formula or if you recall how to do this from the Pythagorean theorem