Here's a solution to a problem I thought of:

How fast does the Earth travel around the Sun?

Find: v
Given: Earth-Sun distance r(ES)=1.50E11 m, t= 1 y = 365 d
s=2(pi)r(ES)=2(pi)(1.50E11 m/1000 m/km)= 9.42E8 km
t=365 d x 24 h/d=8760 h
v=s/t=9.42E8 km / 8760 h = 1.08E5 km/h = 108 000 km/h

metric:s=9.42E8 km x 1000 m/km = 9.42E11 m
t=8760 h x 60 min/h x 60 s/min = 3.15E7 s
v=s/t=9.42E11 m / 3.15E7 s = 2.99E4 m/s = 29 919.9 m/s