The slope is the rise over run. The change in y over the change in x. Pick two points on a line and find the change. It is usually represented by m in the slope intercept form.
Pick two points on a line and use the formula m to find the slope, which represents the rate of change.
431.2+826.4d=2910.4 431.2 is only the first day therefore it doesn't need the variable because the variable represents the number of days. 826.4 even says "each remaining day" referring to what the variable represents.
