# How do you solve by substitution y = 3x + 5 and 4x – y = 5?

Jun 7, 2015

We can substitute the expression for $y$ given to us by the first equation into the second equation:

$5 = 4 x - y = 4 x - \left(3 x + 5\right) = 4 x - 3 x - 5$

$= \left(4 - 3\right) x - 5 = x - 5$

Then add $5$ to both ends to get:

$x = 10$

Then substitute this value of $x$ for $x$ in the first equation:

$y = 3 x + 5 = 3 \cdot 10 + 5 = 30 + 5 = 35$