So I'm currently doing questions on binomial expressions, and I'm not sure as to how to do it after this >.> Any guidance? Thank you :]

This is the question: If , find the value of .

So this was what I tried to do:

I thought that it meant triple (we are currently doing expressions related to ^^)

So this was what I did:

And then I simply substituted as given in the question:

And multiplied, and got the answer:

But I'm pretty sure that what I have done is completely wrong.. any help?