the product of 4x^2y^5 and a certain monomial is 28x^7^9z^2. find the missing monomial factor

Think about a similar but much simpler  problem.

If  The product of 5 and something = 35

then that something is 35/5=7

SO

If the product of 4x^2y^5 and a certain monomial is 28x^7^9z^2

then

the certain polynomial must be  

 $$\\\dfrac{28(x^7)^9z^2}{4x^2y^5}\\\\
\\\dfrac{28x^{63}z^2}{4x^2y^5}\\\\
\\\dfrac{7x^{61}z^2}{y^5}\\\\$$