What is the value of x when -3x + 7x = -12?

Solution:

Given: Equation is 

-3x + 7x = -12

Isolate the variable and solve for x.

⇒ 4x = -12

⇒ x = -12/4

⇒ x = -3

Let us take another example: What is the value of x when 5x - x + 4 = 20?

Given:

5x - x + 4 = 20

⇒ 4x + 4 = 20

Subtracting 4 from both sides we have

⇒ 4x + 4 - 4 = 20 - 4

⇒ 4x = 16

⇒ x = 16/4

⇒ x = 4

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What is the value of x when -3x + 7x = -12?

Summary:

The value of x when -3x + 7x = -12 is -3.