Divide using factorisation:
45(x⁴- 3x³- 28x²) by 9x(x+4)

45(x⁴-3x³-28x²) / 9x (x+ 4)
now take common in numerator
45 * x²(x²-3x - 28) / 9x(x+4)
do cutting of  45x² /9x that is 5x
do middle term spilitting
5x(x²-3x - 28) / x+4
5x [x² -7x +4x -28 ] / x+4
5x[x(x-7)+4(x-7)] /x+4
5x[(x+4) (x-7)] /x+4
now x+4 and x+4 cancel
5x(x-7)
= 5x²-35x
Hope it helps you Inika