The exercise states: "Find dz/dt using the chain rule"

F(x,y) = xLny + yLnx, x=t+1 y=Lnt

My answer:

(Lny+(x/y)) + (Lnx + (y/x))*(1/t)

Book's answer:

(Lny+(y/x)) + (Lnx + (x/y))*(1/t)

I donīt understand why they inverse the x/y division. Could any one help me please? :S