the lowest common denomenator is the least common multipule of the denomenators
denomenator 1 is x^3y
denomenator 2 is xy^4
factor them
denom1=x*x*x*y
denom2=x*y*y*y*y
so the combination of both is
x*x*x*y*y*y*y or x³y⁴
the least common denom is x³y⁴
