Easy# Counting Words, Every Element Appears at Least Once

COMBIN-SXREKQ

Given a set $X$, a word of length $n$ is a list $a_1a_2\ldots a_n$ where $a_i \in X$. Suppose $X = \{f, u, n\}$. How many words of length 6 are there that use every element of $X$ at least once.