For a given product demand, the time-series trend equation is 53 - 4x. The negative sign on the slope of the equation:

We are given product demand, the time-series trend equation is 53 - 4x.

Where, x represents the time over the demand.

We know, slope-intercept of a linear equation

y=mx+b, where m is the slope (some time we call it rate of increase or decrease) and b is y-intercept (fix value).

Let us write given expression in slope-intercept form.

In order to write it in slope-intercept form we need to write x term first.

So, 53 - 4x could be written as - 4x+53.

Here, we have negative sign in front of 4.

That represents, change in demand and because it is a negative number so we could say, demand is getting decrease at the rate 4 over the unit time.