In Problem 12-2, perform an analysis to determine how sensitive the choice of a four-lane bridge built

Question:

In Problem 12-2, perform an analysis to determine how sensitive the choice of a four-lane bridge built now versus a four-lane bridge that is constructed in two stages is to the interest rate. Will an interest rate of 15% per year reverse the initial decision? At what interest rate would constructing the two-lane bridge now be preferred?