Using dimensional analyisis to verify formulae

[BogMonkey]

Heres a question I never figured out.

"Using dimensional analysis, determine which formula (a) or (b) is correct for the description of the force due to gravity between a body of mass m (kg) and another of mass M (kg) separated by a distance of r (m). The gravitational constant G has units (m^3s^-2kg^-1)
(a) FG = G m M / r^2 (b) FG = G m M ./ r"

I've been looking up dimensional analysis but can't find any information relating to validating formulae.

 

[Doc Al]

For an equation to be physically meaningful, the units on each side must match. Check the units in these two and see what you find.