Stuck on Problem 6.2 in Peskin's QFT Book?

[kprkpr]

Homework Statement

In fact this is not homework, I'm self-studying QFT by reading Peskin's book, and I'm stuck with Problem 6.2.

Homework Equations

In part (e), I cannot get the factor (1+(1-x)²)/x in the cross section.

The Attempt at a Solution

Maybe I'd already been wrong in earlier parts, the result I got in part (b) is C~D~\sqrt{EE'}\theta,
and the probability I got in part (c) is ~ \frac{1}{EE'\theta^2}

Generally I just do every problem on this book, but now I'm stuck and can't move on, please please help. Thank you.

 

[vela]

It might help if you posted the original problem and what you've done on it so far.