Solve 6x − 15 = 21

The solution of 6x − 15 = 21 is x = 6.

6x - 15 = 21\ \Rightarrow\ x = 6

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The lines y = 6x − 15 and y = 21 meet at x = 6. 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.
$6x - 15 = 21$
2
Add 15 to both sides:
$6x - 15 + 15 = 21 + 15 \ \Rightarrow\ 6x = 36$
3
Divide both sides by 6:
$\frac{6x}{6} = \frac{36}{6} \ \Rightarrow\ x = 6$
4
Check: put x = 6 back into the equation.
$6\cdot6 - 15 = 36 - 15 = 21 \checkmark$

LaTeX source of the formulas on this page

\[ 6x - 15 = 21\ \Rightarrow\ x = 6 \]
\[ 6x - 15 = 21 \]
\[ 6x - 15 + 15 = 21 + 15 \ \Rightarrow\ 6x = 36 \]
\[ \frac{6x}{6} = \frac{36}{6} \ \Rightarrow\ x = 6 \]
\[ 6\cdot6 - 15 = 36 - 15 = 21 \checkmark \]

Trying values of x in 6x − 15 = 21

x	6x − 15	Equals 21?
4	9	no
5	15	no
6	21	yes
7	27	no
8	33	no

Questions

What is x in 6x − 15 = 21?

The solution of 6x − 15 = 21 is x = 6.

How do you solve 6x − 15 = 21?

Add 15 to both sides to get 6x = 36, then divide both sides by 6 to get x = 6.

How do I check the answer?

Replace x by 6: 6(6) − 15 = 21, which is 21.

Solve 6x − 15 = 21

How to work it out

Trying values of x in 6x − 15 = 21

Questions

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