fix: correct week12 Q3 convergence iteration count

[rwmath27]

Summary

• Correct the answer hint for Week 12 exercise 3.
• The original calculation used ln 10^6, but reducing the error from 100 to 0.01 requires 100 * 0.99^k < 0.01, i.e. 0.99^k < 10^{-4}.

Details

The correct threshold is:

k > ln(10^4) / ln(1/0.99) ≈ 916.42

Therefore the minimum integer number of iterations is 917, not 1380.

Verification

• Checked the derivation from the exercise statement.
• Ran a numerical sanity check for ceil(log(1e-4) / log(0.99)).