$\left. \begin{array}{l l l l} a+e+i=15 \\ b+e+h=15 \\ c+e+g=15 \\ d+e+f=15 \end{array} \right\} \Rightarrow (a+b+c+d+e+f+g+h+i)+3e=60 \Rightarrow 45+3e=60 \Rightarrow e=5$

$\left. \begin{array}{l l} a+e+i=15 \\ c+e+g=15 \end{array} \right\} \Rightarrow a+i+c+g=20$