# How do you solve 4/(b-3.9)=2/(b+1)?

Jul 29, 2017

$\textcolor{g r e e n}{b = - 5.9}$

#### Explanation:

Given
$\textcolor{w h i t e}{\text{xxx}} \frac{4}{b - 3.9} = \frac{2}{b + 1}$

If we multiply both sides by $\left(b - 3.9\right) \left(b + 1\right)$
(sometimes called "cross-multiplying")
we get
$\textcolor{w h i t e}{\text{xxx}} 4 \left(b + 1\right) = 2 \left(b - 3.9\right)$

Expanding
$\textcolor{w h i t e}{\text{xxx}} 4 b + 4 = 2 b - 7.8$

Simplifying
$\textcolor{w h i t e}{\text{xxx}} 2 b = - 11.8$

$\textcolor{w h i t e}{\text{xxx}} b = - 5.9$