So, once again, our X and Y are in different signs. Now, these two guides are isomers to one another, and they're separated by 66 kilotons of mole. So let's look at the following few examples, and let's try to figure out which ones are E and which ones are Z. So we're looking for the heavier groups and the lighter groups. So we have two methyl groups and two Ethyl groups. Ethyl is heavier.