Let $x be the amount of money you spent and $y be the amount of money your brother spent.
1. You both spend a total of $400, then
x+y=400.
2. Your brother spent $80 more than you did, then
y=x+80.
Consider the system of two equations:
[tex]\left\{\begin{array}{l}x+y=400\\y=x+80\end{array}\right..[/tex]
The graphical representation for this system is shown below. The common point is (160,240), this means that you spent $160 and your brothe spent $240.
