Permutation of word with and without Repetition of letters.

I am not sure what your doubt is,

but BELONG has 6 different letters, now different 6 letter word that can formed such that

first 3 letters without repetition and and last three letters with repetition would be

( _ _ _ ) ( _ _ _ ) = (6 * 5 * 4) * (3 * 3 * 3)

After the first 3 slots are filled in 6P3 ways, the remaining 3 letters can be used with repetition for the last 3 slots, so that is 3*3*3

But You are not mixing the two different kind of letters.