The sum of the letters in the first row is 10, and the sum of the letters in the second column is 15.
What is the sum of the letters in the third column?
E+T+A, no matter the order of the variables, is always =10
E+T+T=15, so T-A=5.
E+T+T can be expressed as E+T+A+(T-A), so we see that E+T+A+(T-A)=15, or 10+(T-A)=15, or 10+5=15.
A+E+A can be expressed as E+T+A-(T-A), so it equals 10-5=5.
Your answer is 5.
