How to calculate the orbital period and the density of a planetary body? I'm a student studying in 9th grade, I am making this fictional habitable planet named &quot;Darwin B&quot; for a planet making competition. It orbits a sun-like star at a distance of 1.15 AU or 172 million kilometres in a nearly circular orbit. Its rotational period is 19 hours, 38 minutes. Its mass is $6.15×10^{24}kg$ and its radius is about 6,743 kilometres. I have to calculate its orbital period and density but I'm weak in maths and don't know how to. Please help.
The formula for orbital period is given on Wikipedia:
$$T=2\pi \sqrt\frac{a^3}\mu$$
where:

$T$ is the orbital period in seconds
$a$ is the orbit's semi-major axis in meters
$\mu = GM$ is the standard gravitational parameter

$G$ is the gravitational constant
$M$ is the mass of the more massive body in kilograms



So $T = 2 \pi \sqrt \frac { (172 \cdot 10^9) ^ 3 } { 6.674 \cdot 10^{-11} \cdot 1.9884 \cdot 10^{30} }$. Can you take it from here?
As for density, the volume of a sphere is given by the formula $V = \frac43\pi r^3$; density ($\rho = \frac MV$, with $M$ the mass) is usually given in grams per cubic centimeter, so it makes sense to convert to those units. That gives the following calculation:
$$\frac { 6.15 \cdot 10^{27} } { \frac43\pi (6.743 \cdot 10^8)^3 }$$