-3x + 7x = -12 equals x = -3.
First, simplify -3x + 7x to 4x. / Your problem should look like: 4x = -12.
Second, divide both sides by 4. / Your problem should look like: x = [tex]- \frac{12}{4} [/tex] .
Third, simplify [tex] \frac{12}{4} [/tex] to 3. / Your problem should look like: x = -3, which is your answer.
