(b)
Given differential equation can be rewritten as
$y - x\ \frac{dy}{dx} = \sqrt{a^{2}\ \left( \frac{dy}{dx} \right)^{2} + b^{2}}$
$\Rightarrow$ $y^{2} + \left( x\ \frac{dy}{dx} \right)^{2} - 2yx\ \frac{dy}{dx} = a^{2}\left( \frac{dy}{dx} \right)^{2} + b^{2}$
Here, order is 1 and degree is 2.