have been studying confidence intervals (CI) but I can't get this question.

A 95% CI for a mean mu is 85.3 +/- 2.35. Find the following CI for mu.

(a)90% (b) 99%

I guess that I'd express the 95% explicitly with every thing I know and then use simultaneous equ. maybe to find sigma and n.

If you could help me do one it would be much appreciated.

Thanks, D