Samuel ordered $2$ posts with words only and $2$ posts with pictures only. after placing his order, samuel realized he could have saved money if he, instead, ordered $2$ posts with words and pictures. let $y$ represent samuel's savings, in dollars, and let $x$ represent the number of posts. which equation could be used to determine the amount of money samuel could have saved if he ordered $2$ posts with words and pictures, instead of his original order?