Yes, it helps me thank you very much. Although I forgot one thing, why do the bounds change again?
so pretty much we did a u-sub, and what i did was this:
i let u = 2x-1
now my original integral had the bounds from 1 to 2
so when i did a u-sub here, i have to now say that my 'new' upper bound will be 2x-1, where 'x' was my old upper bound. So now i get a new upper bound as 2(2) - 1 = 3
i do the same to my old lower bound, and i get 2(1) - 1 = 1 , hope that helps