[()]/x^3 divide the x^3 into the polynomial

The given poly. has 3 terms.  You may divide each one by x^3, one at a time.
For example, 3x^4 divided by x^3 equals 3x.  That's the first term of your answer.

Next, divide x^3 into -6x^2.  Writing this out, we get       -6x^2
                                                                                       
                                                                                            x^3

The larger power of x is in the denominator, so the fraction reduces to 

-6

   x

This is your second term.

Try finding the 3rd term (that is, the 3rd quotient).

Write out your final answer in this format:

3x - 6/x - [  ?  ]