What is the y-intercept of a line that has a slope of –3 and passes through point (0, –7)?

   y - y₁ = m(x - x₁)
y - (-7) = -3(x - 0)
   y + 7 = -3(x) + 3(0)
   y + 7 = -3x + 0
       - 7           - 7
          y = -3x - 7
          y = -3(0) - 7
          y = 0 - 7
          y = -7
    (x, y) = (0, -7)

Y=mx+c
y=-3x+c
Replacing for x and y using the given point;
-7=-3(0)+c
c=-7
The y intercept is (-7)

The density of the cube is 40