Answer:
For any two given points (x1,y1) and (x2,y2), the slope = (y2-y1)/(x2-x1)
Let's take the points (15,3) and (30, 6):
slope = (y2-y1)/(x2-x1)
= (6-3)/(30-15)
=3/15
=1/5 =0.2
The slope, in general, means the rate of change of y, relative to x. In the context of this question, the slope tells us that the amount of concrete that can be poured (in yards) is a fifth of the time taken (in minutes).