*Principle of homogeneity
According to principle of homogeneity of quantities (PHQ) only those quantities can be added or subtracted which have same physical nature.
e.g. Force can’t be added in velocity, similarly or distance can’t be subtracted from time.
Also according to PHQ: L + L = L and L – L = L
L + T = not possible and T – M = not possible.
However there is no restriction on multiplication or division i.e. quantities having same or different dimensions can be both multiplied as well as divided. e.g. v = x/t, F = m.a, P = F/A, W = F.x etc.