This document discusses solving systems of linear equations in two variables. There are three main algebraic methods discussed: 1) elimination by substitution, which involves substituting one variable's expression into the other equation to get an equation with just one variable; 2) elimination by equating coefficients, which involves multiplying equations by constants and subtracting to eliminate one variable; and 3) cross-multiplication, which uses cross-multiplication of fractions to eliminate one variable. An example of using elimination by substitution to solve the system x + 2y = -1 and 2x - 3y = 12 is shown.