# How do you solve 3x + 6 = 21?

Feb 29, 2016

$x = 5$

#### Explanation:

$3 x + 6 = 21$

Following the correct rules in math:

Subtract both sides with "-6" to isolate 3x, making the equation looks like this:

$3 x + 6 - 6 = 21 - 6$
$3 x = 15$

Divide both sides by 3 to come up with x, making the equation:

$\cancel{\frac{3 x}{3}}$ = $\cancel{\frac{21}{3}}$

$x = 5$

SHORTCUT METHOD:
This one does not follow the correct rules in math but this is very helpful for "limited time" exams.

$3 x + 6 = 21$

Transfer +6 to other side of the equation, converting the sign to opposite one making +6 to -6

$3 x = 21 - 6$

Subtract

$3 x = 15$

Divide it by the number with $x$

$\cancel{\frac{3 x}{3}} = \cancel{\frac{15}{3}}$

$x = 5$