A jeweler received 8 watches in their respective boxes. He took them out and put them back in. What is the probability that

a-One watch in the right box

b-At most one watch in the right box

c-at least one watch in the right box.....

I knw this involves the derrangments formula, but i dont know how to use it, please teach me, and please dont stretch it, teach me and give me answers too, tomorrow is my exam:S i cant get thru this practice question