Question

solve the system of equations by substitution:
$x + 3y = -15$
$y = -7$

Explanation:

Step1: Substitute $y=-7$ into first equation

$x + 3(-7) = -15$

Step2: Simplify the left-hand side

$x - 21 = -15$

Step3: Solve for $x$

$x = -15 + 21$
$x = 6$

Answer:

$x=6$, $y=-7$ (or the ordered pair $(6, -7)$)