It gets assigned a number one because our double bond begins on carbon one. If we begin number eight, our backbone, from this end, our carbon double bond will get a three. And since we want the lowest possible number value according to step two or rule two, this is how we label it. So we name our alkene simply one. Butane so the in part simply means our double bond is found on the first position and we have a four carbon backbone. So butte means we have a four carbon backbone.