# How do you solve by substitution x + y = 4 and y = 2x + 1 ?

Jun 8, 2015

{x+y=4
{y=2x+1
Take the second and substitute into the first for $y$:
$x + \left(2 x + 1\right) = 4$
$3 x = 3$
$x = 1$
Back into equation 2:
$y = 2 + 1 = 3$
Solution:
$x = 1$
$y = 3$