What is the slope of the line with equation y=9x

y = –9x – 3 (1) 
slope of a line is given by the equation 

y = mx +c 
here m = slope 
compare the equation (1) with the standard form y = mx + c 

we find slope (m) = -9 
To find the y intercept put x = 0 in equation(1) 
y = -9(0) - 3 
y = -3 
hence y intercept = -3 

Density= Mass divided by Volume, but you're trying to find Volume so you apply Algebra and get Volume= Mass divided by Volume.

Volume= 0.5592841163 [kg/m (power to the 3)]

You should round it up