Solve 6x − 12 = 78

The solution of 6x − 12 = 78 is x = 15.

6x - 12 = 78\ \Rightarrow\ x = 15

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The lines y = 6x − 12 and y = 78 meet at x = 15. 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.
$6x - 12 = 78$
2
Add 12 to both sides:
$6x - 12 + 12 = 78 + 12 \ \Rightarrow\ 6x = 90$
3
Divide both sides by 6:
$\frac{6x}{6} = \frac{90}{6} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$6\cdot15 - 12 = 90 - 12 = 78 \checkmark$

LaTeX source of the formulas on this page

\[ 6x - 12 = 78\ \Rightarrow\ x = 15 \]
\[ 6x - 12 = 78 \]
\[ 6x - 12 + 12 = 78 + 12 \ \Rightarrow\ 6x = 90 \]
\[ \frac{6x}{6} = \frac{90}{6} \ \Rightarrow\ x = 15 \]
\[ 6\cdot15 - 12 = 90 - 12 = 78 \checkmark \]

Trying values of x in 6x − 12 = 78

x	6x − 12	Equals 78?
13	66	no
14	72	no
15	78	yes
16	84	no
17	90	no

Questions

What is x in 6x − 12 = 78?

The solution of 6x − 12 = 78 is x = 15.

How do you solve 6x − 12 = 78?

Add 12 to both sides to get 6x = 90, then divide both sides by 6 to get x = 15.

How do I check the answer?

Replace x by 15: 6(15) − 12 = 78, which is 78.

Solve 6x − 12 = 78

How to work it out

Trying values of x in 6x − 12 = 78

Questions

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