A 40-year building programme for new houses began in Oldtown in the year 1951 (Year 1) and finished in 1990 (Year 40).

Anonymous
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The numbers of houses built each year from an arithmetic sequence with a first term a and common difference [/math]d[/math]. Given that 2400 new houses built in 1960 and 600 new houses built in 1990, find the values of a and d.