If the angular momentum of a planet of mass $m$, moving around the sun in a circular orbit is $L$, about the center of the sun, its areal velocity is:

Angular momentum =L
Mass of the Planet =m.
Relation between Angular momentum, mass of the planet and Areal Velocity of the Planet is given by the formula $\mathrm{L}=2\mathrm{m}\times \mathrm{\Delta A}/\mathrm{\Delta t}$

$\frac{∆\mathrm{A}}{∆\mathrm{t}}=\frac{\mathrm{L}}{2\mathrm{m}}$