#### Answer

(a) directly proportional
(b) not proportional

#### Work Step by Step

(a) $y$ is directly proportional to $x$ in the equation $y=3x$, since it has the form of $y=kx$.
(b) $y$ is not proportional to $x$ in the equation $y=3x+1$ because it does not have the form $y=kx$ or $y=k/x$.