Solve 4x − 15 = 57

The solution of 4x − 15 = 57 is x = 18.

4x - 15 = 57\ \Rightarrow\ x = 18

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The lines y = 4x − 15 and y = 57 meet at x = 18. 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.
$4x - 15 = 57$
2
Add 15 to both sides:
$4x - 15 + 15 = 57 + 15 \ \Rightarrow\ 4x = 72$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{72}{4} \ \Rightarrow\ x = 18$
4
Check: put x = 18 back into the equation.
$4\cdot18 - 15 = 72 - 15 = 57 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 15 = 57\ \Rightarrow\ x = 18 \]
\[ 4x - 15 = 57 \]
\[ 4x - 15 + 15 = 57 + 15 \ \Rightarrow\ 4x = 72 \]
\[ \frac{4x}{4} = \frac{72}{4} \ \Rightarrow\ x = 18 \]
\[ 4\cdot18 - 15 = 72 - 15 = 57 \checkmark \]

Trying values of x in 4x − 15 = 57

x	4x − 15	Equals 57?
16	49	no
17	53	no
18	57	yes
19	61	no
20	65	no

Questions

What is x in 4x − 15 = 57?

The solution of 4x − 15 = 57 is x = 18.

How do you solve 4x − 15 = 57?

Add 15 to both sides to get 4x = 72, then divide both sides by 4 to get x = 18.

How do I check the answer?

Replace x by 18: 4(18) − 15 = 57, which is 57.

Solve 4x − 15 = 57

How to work it out

Trying values of x in 4x − 15 = 57

Questions

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