v = 2*pi*R/T,

you have R in m and T is days, which multiplied by 86,400 s/day gives T in seconds.

Then v = 2*pi*3.84*10^8/(27.3*86,400) = 1,022.9 m/s ~ 1 km/s (about 3 times the speed of sound 🙂

For the Earth around the Sun, it would be v = 2*pi*149.5*10^9/(365*86,400)~ 29.8 km/s!

I know it’s not in the problem, but it’s interesting to know how fast the Earth moves around the Sun! And yet we do not feel it (that’s one of the reasons some ancient people thought crazy the Earth not being at the center, there would be such strong winds!)