The equivalent polynomial is 12x^2 -23x - 24.
You can get this by multiplying the two parenthesis by each other.
First start by multiplying the two front numbers:
4x * 3x = 12x^2
Then multiply the outermost numbers:
4x * -8 = -32x
Then multiply the innermost numbers:
3x * 3 = 9x
Then multiply the last numbers:
3* -8 = -24
Now combine all of them to get the above polynomial.