Question

(\begin{cases} y = -5x \\ x + 3y = 28 end{cases})

Explanation:

Step1: Substitute $y=-5x$ into second equation

$x + 3(-5x) = 28$

Step2: Simplify left-hand side

$x - 15x = 28$
$-14x = 28$

Step3: Solve for $x$

$x = \frac{28}{-14} = -2$

Step4: Substitute $x=-2$ into $y=-5x$

$y = -5\times(-2) = 10$

Answer:

$x=-2$, $y=10$