-3x^4 + 27x^2 + 1200 = 0
factor out -3
-3(x^4 -9x^2 -400)=0
divide by -3
x^4 -9x^2 -400=0
(x^2-25) (x^+16) = 0
x^2-25=0 x^2+16=0
(x-5)(x+5)=0 x^2=-16
x=5 x=-5 x = 4i x=-4i
Answer: x=5 x=-5 x = 4i x=-4i
You need to subtract 25 by 18
Slope = -2/1
work is provided in the image attached.
The density would be 5.11111111.... and so on g/cm^3. I don't know how far your teacher wants you to round.