Answer
$y=10$
Work Step by Step
We set up a proportion, using $\frac{x_1}{y_1}=\frac{x_2}{y_2}$, where $x_1$ and $y_1$ represent the $x$ and $y$ values in the problem, and $x_2$ and $y_2$ represent the new values.
In this case, we don't know what $y_2$ is, so we will represent that as $y$.
We set up the proportion to get
$\frac{15}{25}=\frac{6}{y}$
Cross multiplying gives
$15y=150$
To isolate $y$, we divide both sides by 15, giving
$y=10$
