Answer:
The image is so blurred
Step-by-step explanation:
Please tell me all the measures used in your question or re ask your question and instead screen shot
There are two ways to find the total with tax
Either you can do
cost + cost x tax rate
or
cost x (1+tax rate)
Since the second one requires less steps, it's easier to do that.

The cost with tax is
$17.27
Hello,
12x^4+39x^3+9x²=x²(12x²+39x+9)=x²(12x²+36x+3x+9)=x²(4x(3x+9)+(3x+9))
=x²(3x+9)(4x+1)
=3x²(x+3)(4x+1)