3.simplify the expression. 9xy2 – 11xy2 show your work

Ok so 9x minus 11x you get -2x then the two y^2 cancel each other out to get -2x if the y^2 is separate from the x variable. However if its all one then it would be just 9 minus 11 to get -2 then putting the variable back on the end to get -2xy^2.