Write down the $y$-intercept of $\ell$ and determine its gradient.

The line $m$ is parallel to $\ell$ and passes through $P(2,1)$ Determine the equation of $m$ in the form $y=mx+c$

The line $n$ is perpendicular to $\ell$ and passes through the point where $m$ intersects the $y$-axis. Determine the equation of $n$ in the form $Ax+By+C=0$ where $A,B,C$ are integers with no common factor and $A>0$