Okay, so my book is horrible and it doesnt explain things very well and i cant seem to find my answer anywhere online.

I wont write out the example in the book since i think its irrelevant and way to long. I am struggling with the notation and how they get the answer.

I m very confused on how they got the answer.

I think the (3 0 ) = 0?

Can someone please explain and

work this out because i am completely lost and i am sure its easy.

I am wiling to look at a webpage if i knew what to look up.

Thank you