In future, if you want me to answer then you must ask in the Ask the Tutor Forum (this forum is for students to help each other). (And please do not write in capital letters!)
The answer in the lecture notes is completely correct.
I assume that you have watched my free lectures explaining part (a) of the example (otherwise it would be pointless using the lecture notes). The approach in part (b) is exactly the same and the workings are shown in the printed answer. The demand increases by 33.33% and the price falls by 3.33%. 33.33/3.33 = 10. I have no idea how you have arrived at 30.