# How do you solve x + y = 12, y =2x using substitution?

$x = 4 \mathmr{and} y = 8$
$x + y = 12 \to y = 12 - x$
$y = 2 x$
which means $12 - x = 2 x \to 3 x = 12 \to x = 4$
$y = 2 \cdot 4 = 8$