How to solve this equation?

Question

I already know that result is $72$ , but I don't know how to solve this on paper.

$x=9+\dfrac{y}{2}$

$y=9+x$

$9+x+y=72$

So, how I can solve $x$ and $y$ ? Any help? :)

Answer 1

From equation 3, $x + y = 63$

From equation 2, $y = 9 + x$, so:

$x + (9 + x) = 63$

$2x + 9 = 63$

$x = 27$

$y = 36$

Notice that the solution satisfies all three equations.