Answer:
or 
Step-by-step explanation:
Substitution means plugging in one variable's value that consists of the opposite variable. Because
is already specified, you can plug it into the second equation's
value. After doing that, it looks like this:

Then you would distribute the
across the parentheses next to it, like this:

Then, add like terms, like this:

Then divide both side by
to isolate
.

Now, you can plug
(
) into either equation, but the first one seems simpler so you would pick that. It would look like this:

Solving would look like this:

So the answer is
or
.