p-n junction problems

I've attached a formula sheet and two problems I've been working on.  Please look over and correct where I went wrong.

[1] Consider a silicon p-n junction at 300K.  The p side is doped with acceptors only, with Na=6x10^16cm^-3.  The n side is doped with donors only, with Nd=2x10^16cm^-3.

Find Vbi.  Next, It is desired to increase Vbi by .04V by adding donors to one side of the existing junction.  To which side should they be added, and in what concentration?

[2] Consider a silicon p-n junction in which the depletion rgion on the n side is 10 times larger than the depletion width on the p side on the p side.  Assume Vbi=.770V.

Find Na and Nd.  Find W for zero bias.  For what value of reverse bias with Cj=3.0x10^-9 F/cm^2.

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For 2a, I could not explicitly find Xn or Xp so the answer includes Xn for Nd and Na.  I am reasonably certain these answers are not correct especially when I tried to plug in xn and xp from part b into part a.

For part 2a, I am assuming zero bias because Va was not given.  So, I just used zero.  I also used 1 for e because it doesn't need to be converted to other units (in both problems 1 and 2).  For part C, I've completely lost faith in my values for Nd and Na and didn't even plug them in.

Thank you.