# How do you solve for x in 90e^(-.879x)=225?

$x = \ln \frac{0.4}{0.879} = - 1.042424$, nearly.
Here, ${e}^{0.879} = \frac{90}{225} = 0.4$
So, $x = \ln \frac{0.4}{0.879} = - 1.042424$, nearly