How do I work this problem, I am confused?

2 radical [72] + radical [32] - 4 radical [18]

Are radicals just square roots?
If so just put it in your calculator?

(I've never come across the term radical in mathematics before - is it an american thing?)

Capuchin: this seems like a reoccurring theme. Some interesting info here:
http://www.und.nodak.edu/instruct/lgeller/radical.html

Okay, so do you think the OP just confused over what radical meant?

I don't think so. I think they know that radical is square root in that case. I think they don't understand how to work with roots.

I think the main thing they should understand is that they need to factor the number inside the radical into primes and then find pairs of factors and pull them out (that's the best way I can explain it though not exactly how I would do it)
For example:
Radical[72]
Find prime factors
Radical[3*3*2*2*2]
Pull out factor pairs (they go from pairs inside the radical to single multipliers outside)
3*2*radical[2]
Simplify
6*radical[2]

If the OP does this process for all 3 terms they should see a way to further simplify.

Aye, the OP should also be reminded to slap their teacher for using the term radical.

Aha, "radical" is a term used to desribe the symbol you are thinking of. It is not only used for a square root, but also for a quadratic equation.