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Hi. The correct answer is B. Let me explain why I came to this conclusion.

I like starting from the end of the equation to the front. As most know, when we divide exponents, we subtract them. 

y^13-y^9 = y^4
x^5 + x^8=x^13
Because I can only simplify using positive exponents, I transformed ^-5 to ^+5

Now, 72/16 = 4.5. I multiplied 4.5 by 2 and came out with 9. Because I multiplied 4.5, the answer would have to be a fraction. 
So now we are left with 9y^4/2x^13

Provide an equation