Suppose that you need to solve the following system.

Equation A: $\displaystyle{3}{x}+{6}{y}={12}\usepackage{cmbright}\Huge\$

Equation B: $\displaystyle-{3}{x}+{5}{y}=-{1}\usepackage{cmbright}\Huge\$

If you are using the elimination method to get rid of one of the variables, which is the most efficient first step?