Need help writing a formula to find the probability that your final withdrawal is below 50% of what you would like to be able to withdraw. Any help is appreciated. Thank you.

You just retired with $3,400,000 savings. You plan to withdraw money from your account at the beginning of each year to live on, and would like to withdraw $$156,000 the first year and then increase the withdraw amount enough each year to keep up with inflation. You plan to invest 50% of your funds in a risk free account that will earn 3.9% per year and the rest in a risky portfolio where you expect the returns to follow a lognormal distribution with a mean of 8.1% and a standard deviation of 16.8%. You are concerned that if your risky portfolio underperforms you will run out of money, so you are considering limiting the withdraws to a percentage of the money in your account at the start of the year. Use Monte Carlo simulation to estimate the probability that your final withdraw will be less than half of what you would like to withdraw using different withdraw limits. Assume you will be retired for 26 years. ( 50 points total)