4y to the 5th power 81q to the 7th power

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9q to the 2nd power 16y .

4y^5*81q^7/(9q^2*16y)= do the coefficents first, then the powers

4*81/16*9=
9/4

y^(5-1)q^(7-2)

9y^4 q^5 /4

check that.