Solve 3x − 15 = 18

The solution of 3x − 15 = 18 is x = 11.

3x - 15 = 18\ \Rightarrow\ x = 11

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The lines y = 3x − 15 and y = 18 meet at x = 11. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

1
The goal is to get x alone. Undo the operations in the opposite order: first the subtraction, then the multiplication.
$3x - 15 = 18$
2
Add 15 to both sides:
$3x - 15 + 15 = 18 + 15 \ \Rightarrow\ 3x = 33$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{33}{3} \ \Rightarrow\ x = 11$
4
Check: put x = 11 back into the equation.
$3\cdot11 - 15 = 33 - 15 = 18 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 15 = 18\ \Rightarrow\ x = 11 \]
\[ 3x - 15 = 18 \]
\[ 3x - 15 + 15 = 18 + 15 \ \Rightarrow\ 3x = 33 \]
\[ \frac{3x}{3} = \frac{33}{3} \ \Rightarrow\ x = 11 \]
\[ 3\cdot11 - 15 = 33 - 15 = 18 \checkmark \]

Trying values of x in 3x − 15 = 18

x	3x − 15	Equals 18?
9	12	no
10	15	no
11	18	yes
12	21	no
13	24	no

Questions

What is x in 3x − 15 = 18?

The solution of 3x − 15 = 18 is x = 11.

How do you solve 3x − 15 = 18?

Add 15 to both sides to get 3x = 33, then divide both sides by 3 to get x = 11.

How do I check the answer?

Replace x by 11: 3(11) − 15 = 18, which is 18.

Solve 3x − 15 = 18

How to work it out

Trying values of x in 3x − 15 = 18

Questions

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