Capital gain calculation

I sold about two thirds of an acre of ground to a local authority for 70K in Feb this year and I want to calculate the gain. There's about a half acre left (on which stands my PPR.). I had purchased the whole site in 1996 for twenty thousand Irish pounds. What is the calculation of gain? If I had spent money in 1998 & 99 in putting in a new water suppy (project cost approx 14K) would that be deductible...what rate tax on gain?

Thanks...