Window size of working set $= 4$
Initial pages in the working set window $= \{ e, d, a\}$
$$\small \begin{array}{|c|c|c|c|}\hline \textbf{Incoming page} & \textbf{Time} & \textbf{Working set window} & \textbf{Hit/ Miss} & \textbf{Current window size} \\\hline c & 1 & \{ e, d, a, c\} & \textbf{miss} & 4 \\\hline c & 2 & \{ d, a, c\} & \text{hit} & 3 \\\hline d & 3 & \{ a, c,d\} & \text{hit} & 3 \\\hline b & 4 & \{ c,d,b\} & \textbf{miss} & 3 \\\hline c & 5 & \{ d, b, c\} & \text{hit} & 3 \\\hline e & 6 & \{ d,b,c,e \} & \textbf{miss} & 4 \\\hline c & 7 & \{ b, c,e\} & \text{hit} & 3 \\\hline e & 8 & \{c,e\} & \text{hit} & 2 \\\hline a & 9 & \{c,e,a \} & \textbf{miss} & 3 \\\hline d & 10 & \{c,e,a,d \} & \textbf{miss} & 4 \\\hline \end{array}$$
Total number of page faults $=\mathbf{ 5}$.
Average no. of page frames used by window set $= ( 4 + 3 + 3 + 3 + 3 + 4 + 3 + 2 + 3 + 4) / 10 = 32/10 = \mathbf{3.2}$