An arithmetic progression has the first term (a) and the common difference (d) a: write down the third, ninth and the twenty fifth terms of the progression
b: the arithmetic progression above is such that it is increasing and that the third, ninth and the twenty fifth terms form the first three consecutive terms of a geometric progression. The sum of the 7th and twice the sixth terms of the arithmetic progression is 78 calculate the first term and and the common difference of the arithmetic progression ​