If you really don't know then you must read your notes/book again, and again, again...

For example, it is "gcd" = greatest common divisor and not gsd, and for example in gcd(3,24) they're asking you what's the (positive) greatest number that divides both 3 and 24...can you answer this directly?

Now, there's a method to solve this called Euclides Algorithm...either read it in your book or google it.

Tonio