When solving a system by substitution, you start by solving for one of the variables in one of the equations.
It is easier if you look for a variable with a coefficient of 1 or -1, meaning that you look for a variable that does not have a number in front, at most it has a + or - sign.
For example,
in , it is easiest to solve for ,
while in , it is easiest to solve for .
Solving for the variable gives you an expression for that variable as a function of the other variable(s).
Then you substitute that expression into the other equation(s).
Solving for in is the easiest way to start: --> (subtracting from both sides of the equal sign.
Next we substitute for in : --> (applying the distributive property) --> (doing the indicated operations) -->--> (subtracting from both sides) -->--> (taking out as a common factor, sometimes called "collecting like terms") -->--> (dividing both sides by 4)
Now we substitute for in the solved-for-y equation above: -->-->
