I have attached my question. I did the first part " A pension plan is obligated to make disbursements of $1 million, $2 million, and $1 million at

I have attached my question. I did the first part " A pension plan is obligated to make disbursements of $1 million, $2 million, and $1 million at the end of each of the next three years, respectively. Find the duration of the plans obligations if the interest rate is 10% annually."--- I do not know how to solve this part ". If the level of interest rates goes down by 50 basis points (one basis point is 0.01%), how much do you expect the pension plans obligation to go up (in percentage terms)?" Also could you please show your work.( I am not allowed to use a financial calculator)