A ball is thrown vertically upward with an initial velocity of $150 \mathrm{~m} / \mathrm{s}$. The ratio of velocity after $3 \mathrm{~s}$ and $5 \mathrm{~s}$ is $\frac{x+1}{x}$. The value of $x$ is ___________.

$\left\{\right.$ take, $\left.g=10 \mathrm{~m} / \mathrm{s}^{2}\right\}$