# How do you solve the following system?: 3x +y =15 , -9x +8y = 4

Jul 30, 2016

There are many ways to solve this.I'm using substitution method.
lets see:

#### Explanation:

$3 x + y = 15$
$\implies y = 15 - 3 x \left(e q u a t i o n 1\right)$

putting the value of y in equation 2
$- 9 x + 8 \left(15 - 3 x\right) = 4$
$\implies - 9 x + 120 - 24 x = 4$
$\implies - 33 x = - 116$
$\implies x = \frac{- 116}{-} 33$
$\implies x = 3.51$

putting the value of x in equation 1
$y = 15 - 3 \cdot 3.51$
$\implies y = 15 - 10.53$
$\implies y = 4.47$

$\therefore x = 3.51 \mathmr{and} y = 4.47$