MATH116 Lecture 4: info

I need to know if I did this right Please let me know

I know the answer is as follows but I cannot work out the steps involved, it"s killing me! Thank you in advance.

Would someone be able to show me how to go about obtaining theanswer for this problem. I know you're supposed to substitute u forthe denominator but how do I get rid of the x in 6x^2? Any helpwould be awesome. Thanks in advance.