Answer
(a) $y$ is directly proportional to $x$
(b) $y$ is not proportional to $x$
Work Step by Step
RECALL:
(i) If the quantities (or variables) $x$ and $y$ are related by the equation $y=kx$, then $y$ is directly proportional to $x$.
(ii) If the quantities (or variables) $x$ and $y$ are related by the equation $y=\dfrac{k}{x}$, then $y$ is inversely proportional to $x$.
(a)
The given equation is in the same form as in (i) above so $y$ is directly proportional to $x$
(b)
The given equation is not similar to the equations in (i) and (ii) above so $y$ is not proportional to $x$.