Solve 3x + 9 = 51

The solution of 3x + 9 = 51 is x = 14.

3x + 9 = 51\ \Rightarrow\ x = 14

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The lines y = 3x + 9 and y = 51 meet at x = 14. 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 addition, then the multiplication.
$3x + 9 = 51$
2
Subtract 9 from both sides:
$3x + 9 - 9 = 51 - 9 \ \Rightarrow\ 3x = 42$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{42}{3} \ \Rightarrow\ x = 14$
4
Check: put x = 14 back into the equation.
$3\cdot14 + 9 = 42 + 9 = 51 \checkmark$

LaTeX source of the formulas on this page

\[ 3x + 9 = 51\ \Rightarrow\ x = 14 \]
\[ 3x + 9 = 51 \]
\[ 3x + 9 - 9 = 51 - 9 \ \Rightarrow\ 3x = 42 \]
\[ \frac{3x}{3} = \frac{42}{3} \ \Rightarrow\ x = 14 \]
\[ 3\cdot14 + 9 = 42 + 9 = 51 \checkmark \]

Trying values of x in 3x + 9 = 51

x	3x + 9	Equals 51?
12	45	no
13	48	no
14	51	yes
15	54	no
16	57	no

Questions

What is x in 3x + 9 = 51?

The solution of 3x + 9 = 51 is x = 14.

How do you solve 3x + 9 = 51?

Subtract 9 from both sides to get 3x = 42, then divide both sides by 3 to get x = 14.

How do I check the answer?

Replace x by 14: 3(14) + 9 = 51, which is 51.

Solve 3x + 9 = 51

How to work it out

Trying values of x in 3x + 9 = 51

Questions

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