first, let me write the expression

So, the "-" minus before a parenthesis change the signs of the numbers that are inside, so: (and then the parenthesis can go away)

now we can sum or subtract the numbers with the same x, so we can sum the 4x^3 with the -2x^3, the 7x with the x, and the -4 with the 8
so we have

So the answer is: Option B