You are in the wrong subject, but I'll answer the question, but it really belongs in math. The answer is
10!/(4! 2!)
Step-by-step explanation
If the letters were all different and you were to use all of them, then the number of arrangements for 10 letters is 10! (read that as 10 factorial. It means 10*9*8*7*6*5*4*3*2*1
There are 4s. It does not matter which one you pick to go where so you get rid of the duplicates that reflects the fact that you could pick any one of the 4 s. So you divide by 4!
There are 2 o s . You divide by 2 for the same reason.