Question

using the substitution method, vito is solving the following system of equations algebraically:
$y + 3x = -4$
$2x - 3y = -21$
which equivalent equation could vito use?
a $2x - 3(-3x - 4) = -21$
b $2(3x - 4) + 3x = -21$
c $2(-3x - 4) + 3x = -21$
d $2x - 3(3x - 4) = -21$

Explanation:

Step1: Isolate $y$ from first equation

$y = -3x - 4$

Step2: Substitute $y$ into second equation

Substitute $y=-3x-4$ into $2x - 3y = -21$:
$2x - 3(-3x - 4) = -21$

Answer:

A. $2x - 3 (-3x - 4) = -21$