Solve 7x − 15 = 90

The solution of 7x − 15 = 90 is x = 15.

7x - 15 = 90\ \Rightarrow\ x = 15

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The lines y = 7x − 15 and y = 90 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.
$7x - 15 = 90$
2
Add 15 to both sides:
$7x - 15 + 15 = 90 + 15 \ \Rightarrow\ 7x = 105$
3
Divide both sides by 7:
$\frac{7x}{7} = \frac{105}{7} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$7\cdot15 - 15 = 105 - 15 = 90 \checkmark$

LaTeX source of the formulas on this page

\[ 7x - 15 = 90\ \Rightarrow\ x = 15 \]
\[ 7x - 15 = 90 \]
\[ 7x - 15 + 15 = 90 + 15 \ \Rightarrow\ 7x = 105 \]
\[ \frac{7x}{7} = \frac{105}{7} \ \Rightarrow\ x = 15 \]
\[ 7\cdot15 - 15 = 105 - 15 = 90 \checkmark \]

Trying values of x in 7x − 15 = 90

x	7x − 15	Equals 90?
13	76	no
14	83	no
15	90	yes
16	97	no
17	104	no

Questions

What is x in 7x − 15 = 90?

The solution of 7x − 15 = 90 is x = 15.

How do you solve 7x − 15 = 90?

Add 15 to both sides to get 7x = 105, then divide both sides by 7 to get x = 15.

How do I check the answer?

Replace x by 15: 7(15) − 15 = 90, which is 90.

Solve 7x − 15 = 90

How to work it out

Trying values of x in 7x − 15 = 90

Questions

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