Can anybody help explain my equation (simplification / Re arranging issue)

Hello

Please may you help explain my simplification / re arranging issue?

Per my pic I am at the point of the equation where I have posted the red highlight. I understand how the p follow to the next part of the equation, however can someone please explain why my equation does not go to 2y in the next line? I have circled the y that I mean!

Any help much appreciated very much and look forward to hearing from you and understanding this!