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Solve 3x + 12 = 21

The solution of 3x + 12 = 21 is x = 3.

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The lines y = 3x + 12 and y = 21 meet at x = 3-22468510152025303540x = 3y = 3x + 12y = 21
The lines y = 3x + 12 and y = 21 meet at x = 3. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

  1. 1

    The goal is to get x alone. Undo the operations in the opposite order: first the addition, then the multiplication.

    3x+12=213x + 12 = 21
  2. 2

    Subtract 12 from both sides:

    3x+12−12=21−12 ⇒ 3x=93x + 12 - 12 = 21 - 12 \ \Rightarrow\ 3x = 9
  3. 3

    Divide both sides by 3:

    3x3=93 ⇒ x=3\frac{3x}{3} = \frac{9}{3} \ \Rightarrow\ x = 3
  4. 4

    Check: put x = 3 back into the equation.

    3⋅3+12=9+12=21✓3\cdot3 + 12 = 9 + 12 = 21 \checkmark
LaTeX source of the formulas on this page
\[ 3x + 12 = 21\ \Rightarrow\ x = 3 \]
\[ 3x + 12 = 21 \]
\[ 3x + 12 - 12 = 21 - 12 \ \Rightarrow\ 3x = 9 \]
\[ \frac{3x}{3} = \frac{9}{3} \ \Rightarrow\ x = 3 \]
\[ 3\cdot3 + 12 = 9 + 12 = 21 \checkmark \]

Trying values of x in 3x + 12 = 21

x3x + 12Equals 21?
115no
218no
321yes
424no
527no

Questions

What is x in 3x + 12 = 21?

The solution of 3x + 12 = 21 is x = 3.

How do you solve 3x + 12 = 21?

Subtract 12 from both sides to get 3x = 9, then divide both sides by 3 to get x = 3.

How do I check the answer?

Replace x by 3: 3(3) + 12 = 21, which is 21.

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    Solve 3x + 12 = 21: x = 3 (steps and check) | WordGPT