What to keep in mind when solving equations:
Keep the equations balanced (do on both sides)
Isolate the variable (undo what you see)
If you have parentheses - open them before you start solving (by applying Distributive Property)
Verify that your answer is correct (by substituting it back to the equations to see if it works)
Systems of Equations
Introduction - what is it? What does it mean in real life?
Methods to solve - Elimination & Substitution