4. Find $a+b+c+d+e$ if
$$
\begin{array}{c}
3 a+2 b+4 d=10 \\
6 a+5 b+4 c+3 d+2 e=8 \\
a+b+2 c+5 e=3 \\
2 c+3 d+3 e=4, \text { and } \\
a+2 b+3 c+d=7
\end{array}
$$
Solution: Adding the first, third, and fifth equations, we get $5 a+5 b+5 c+5 d+5 e=$ $10+3+7 \Rightarrow a+b+c+d+e=4$.