Eight different letters of an alphabets are given. Words of four letters from these are formed. The number of such words with at least one letter repeated is :

Question

$$\begin {array} {1 1} (a)\;\begin{bmatrix} 8 \\ 4 \end{bmatrix}- ^8 P_4 & \quad (b)\;8^4 + \begin{bmatrix} 8 \\ 4 \end{bmatrix} \\ (c)\;8^4 - ^8P_4 & \quad (d)\;8^4-\begin{bmatrix} 8 \\ 4 \end{bmatrix} \end {array}$$