Answer
See the explanation below.
Work Step by Step
(a) The first-order differential equation is given by:
$k(x,y)=\dfrac{dy}{dx}$
where, $k(x,y)$ denotes a function of two variables which are defined on a region in the xy-plane.
(b) A solution can be defined as a function $y=f(x)$ that satisfies the first-order differential equation $\dfrac{dy}{dx}=k(x,y)$. In order to do that, the function $f(x)$ and its first-order derivative must be substituted into that equation.
