given third term of AP is 7

So, a + 2d = 7…(i)

It is also given that the seventh term exceeds 3 times the third term by 2

To find: first term, the common difference and the sum of the first 20 terms

a + 6d - 3(a + 2d) = 2

- 2a = 2

a = - 1

d = 4

we know that the sum of AP is given by the formula:

substituting the values in above equation

s = 740