Question

solve the system by substitution.
$-5y = x$
$3x + 9y = 24$

Explanation:

Step1: Substitute $x=-5y$ into 2nd equation

$3(-5y) + 9y = 24$

Step2: Simplify left side

$-15y + 9y = 24$
$\implies -6y = 24$

Step3: Solve for $y$

$y = \frac{24}{-6} = -4$

Step4: Substitute $y=-4$ into $x=-5y$

$x = -5(-4) = 20$

Answer:

$x=20$, $y=-4$