Write in equation of the line in the graph

To write the equation of a line, we use the equation: y = mx +b.

m is the slope of the line, which can be calculated using the equation:
m = (y2 - y1)/(x2 - x1) 
We can choose any two points on the line to put into this equation. The red dots are at (0,0) and (-6,-2), so we will use those, but you would get the same answer by using any other pair of coordinates on the blue line.
m = (-2 - 0)/(-6 - 0) = 2/6 = 1/3

b is the y-intercept of the line. The y-intercept is the y-coordinate when the line crosses the y-axis. It crosses the y-axis at (0,0), so the y-intercept is 0.

Now, we plug our values back into the full equation to get the equation of the line.
y = mx + b
y = (1/3)x + 0 

So the final answer is y = (1/3)x or y = x/3, depending on how you want to write it.

Y=3x because it passes through the origin (has b (or y-intercept) 0), and slope of 3

The density of the cube is 40