The speed of light is 300,000 kilometers per second (I have taken the liberty of rounding off slightly)

What is the speed of light in furlongs per fortnight?

You will need these conversion factors
8 furlong (fu) = 1 mile (mi)
1 fortnight (fo) = 14 days (d)
5280 feet (ft) = 1 mile (mi)
1 d = 86400 seconds (s)
1 kilometer (km) = 1000 meters (m)
1 m = 3.28 ft

multiplying them all together…

[(3x10^5 km/s) x (1x10^3 m/km) x (1.4x10^1 d/fo ) x (8.64x10^4 s/d) x (8 fu/mi) x (3.28 ft/m)] /(5.28×10^3 ft/mi) =

You’ll see how the last term has to be divided to make the units come out right.
And separating and multiplying all the powers of 10 by adding up the exponents,
and isolating all the units…

(3 x 1 x 1.4 x 8.64 x 8 x 3.28 / 5.28)x 10^10 (km/s m/km d/fo s/d fu/mi ft/m mi/ft) =

multiplying out and cancelling out the units

180.34×10^10 ( 1/fo fu ) and simplifying and putting in standard form,

1.8034×10^12 fu/fo

The dimensional analysis not only allows you to separate the powers of ten calculations from the numerical ones, it also provides a check on your logic by ensuring the result comes out in the proper units (in this case, a unit of velocity).

If the answer had come out in units of say, seconds per meter, then obviously something went wrong in the setup or computation.