Answer
$ -x^3+x^2-x+4.$
Work Step by Step
We divide each term of the polynomial by the monomial as follows
$$
\frac{bx^4 - bx^3 + bx^2 - 4bx}{-bx }= \frac{bx^4 }{-bx }+ \frac{ - bx^3 }{-bx }+ \frac{ bx^2 }{-bx }+ \frac{ - 4bx}{-bx }\\
=-x^3+x^2-x+4.
$$
