Question 13
Let $A,B,\ldots,I$ be unknowns satisfying
$$\begin{aligned}A+B+C&=1,\\B+C+D&=2,\\C+D+E&=3,\\D+E+F&=4,\\E+F+G&=5,\\F+G+H&=6,\\G+H+I&=7.\end{aligned}$$
What is the value of $A+E+I$?
$$\begin{aligned}A+B+C&=1,\\B+C+D&=2,\\C+D+E&=3,\\D+E+F&=4,\\E+F+G&=5,\\F+G+H&=6,\\G+H+I&=7.\end{aligned}$$
What is the value of $A+E+I$?