How do I simplify 3√300 + 2√27

I was sick today,so I didn't go to school.Being absent doesn't excuse me from the assignment though,since I have internet access.Today's lesson was about simplifying radical expressions like the one above.I've read the chapter,but I still don't understand.Could somebody explain this to me?

First, you simplify the radicals. sqrt300 is simplified to 10 sqrt 3 and sqrt 27 is simplified to 3 sqrt 3.

Then you multiply 3 x 10sqrt3 and get 30sqrt3 and 2 x 3sqrt3 is 6sqrt3.

Last, 30sqrt3 + 6sqrt3 = 363.

The answer is 36squareroot3.