# The local historical society has leased a castle to use it as a museum. The original lease was 99 years. I asked the curator how much time was left on the lease. His answer was as follows: two-thirds of the time past is equal to four-fifths of the time to come. How much time was left on the lease?

Let X equal the time left on the lease (which makes "time past" equal to 99-X). Set up the equation:

2/3 * (99-X) = 4/5 * X

Solve for X to get the answer.