5. A 40-year building programme for new houses began in Oldtown in the year 1951 (Year 1) and finished in 1990 (Year 40).
The numbers of houses built each year form an arithmetic sequence with first term \(a\) and common difference \(d\).
Given that 2400 new houses were built in 1960 and 600 new houses were built in 1990, find
- the value of \(d\),
- the value of \(a\),
- the total number of houses built in Oldtown over the 40-year period.