The medicine was too expensive for me to afford it.
My practice question marked that as wrong for I didn't put the It out at the last. It suggested me to use "...too expensive for me to afford". I couldn't grasp the idea why would that matter. I googled them, but people use the equivalent states as they are with it in the last. Besides I'm not sure there's any wrong in the sentence below as well.
It's too hard to do it alone.
Do I also have to rephrase it into like "It's too hard to do alone"?