The graph of the function
is
- concave upward, when

- concave downward, when

Find 
1.

2.

Now:
1. when
the graph of the function is concave upward and this is for

2. when
the graph of the function is concave downward and this is for

Answer: Density = 1,282.26 kg/m^3
Step-by-step explanation:
Density = 80 lb/ft^3
We know that:
1lb = 0.4536 kg.
1ft^3 = 0.0283 m^3
then we can write:
1 = (0.4536kg)/(0.0283 m^3)*(1ft^3/lb)
we can multiply our equation by this, and it wont be affected, then we have:
Density = 80 lb/ft^3 = 80 lb/ft^3 (0.4536kg)/(0.0283 m^3)*(1ft^3/lb)
Density = 1,282.26 kg/m^3
Is a polynomial
hope this helped
-4 is the x-intercept for your equation