Solve 9x − 15 = 84

The solution of 9x − 15 = 84 is x = 11.

9x - 15 = 84\ \Rightarrow\ x = 11

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The lines y = 9x − 15 and y = 84 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.
$9x - 15 = 84$
2
Add 15 to both sides:
$9x - 15 + 15 = 84 + 15 \ \Rightarrow\ 9x = 99$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{99}{9} \ \Rightarrow\ x = 11$
4
Check: put x = 11 back into the equation.
$9\cdot11 - 15 = 99 - 15 = 84 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 15 = 84\ \Rightarrow\ x = 11 \]
\[ 9x - 15 = 84 \]
\[ 9x - 15 + 15 = 84 + 15 \ \Rightarrow\ 9x = 99 \]
\[ \frac{9x}{9} = \frac{99}{9} \ \Rightarrow\ x = 11 \]
\[ 9\cdot11 - 15 = 99 - 15 = 84 \checkmark \]

Trying values of x in 9x − 15 = 84

x	9x − 15	Equals 84?
9	66	no
10	75	no
11	84	yes
12	93	no
13	102	no

Questions

What is x in 9x − 15 = 84?

The solution of 9x − 15 = 84 is x = 11.

How do you solve 9x − 15 = 84?

Add 15 to both sides to get 9x = 99, then divide both sides by 9 to get x = 11.

How do I check the answer?

Replace x by 11: 9(11) − 15 = 84, which is 84.

Solve 9x − 15 = 84

How to work it out

Trying values of x in 9x − 15 = 84

Questions

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