# How do you solve (3x - 7) - 5( x - 4) = 21?

Mar 18, 2018

x=-4

#### Explanation:

[0] $\left(3 x - 7\right) - 5 \left(x - 4\right) = 21$
First let's simplify by a product rule the term $5 \left(x - 4\right)$
[1] $\left(3 x - 7\right) - 5 \cdot x - \left(5 \cdot - 4\right) = 21$
We also have $- a \cdot - b = a \cdot b$, so:
[2] $\left(3 x - 7\right) - 5 x + 20 = 21$
Parenthesis on $\left(3 x + 7\right)$ are useless, so we have :
[3] $3 x - 7 - 5 x + 20 = 21$
Let's put all numbers on the right part:
[4]$3 x - 7 + 7 - 5 x + 20 - 20 = 21 + 7 - 20$
[5]$- 2 x = 8$
Finally let's Just divide by-2
[6]$x = - 4$

Mar 18, 2018

$x = - 4$

#### Explanation:

We can start by distributing the $- 5$ to the $\left(x - 4\right)$ term. We get:

$3 x - 7 - 5 x + 20 = 21$

We can combine like terms to get:

$- 2 x + 13 = 21$

We can subtract $13$ from both sides to get:

$- 2 x = 8$

Lastly, we can divide both sides by $- 2$ to get:

$x = - 4$

Hope this helps!